RESEARCH REPORTS
MANAGEMENT/PHYSIOLOGY
Continuing Projects
Tree Pruning Studies to Improve the Production and Harvesting of Florida Oranges
Project No. 951-23
Length of Project: 3-5 years
This report is for Year Number 4
Investigators: J.D. Whitney
T.A. Wheaton
W.S. Castle
D.P. H. Tucker
J.K Burns
IFAS - Lake Alfred
R.E. RouseIFAS - Immokalee
Abstract
Controlling tree size and maintaining good fruit production have been a problem in some orange plantings, particularly in cases where vigorous scion/rootstock combinations have been planted at close tree spacings. Fruit production is usually high early in the life of these plantings, and then becomes marginal after the trees have reached containment size. Low fruit production not only reduces gross returns but further reduces net returns because the per box harvesting costs can be higher.
In recent years, tree skirting has become a more common practice, particularly in fruit destined for the fresh market. In the last 5 seasons, tree skirting has been necessary to accommodate new shake-catch mechanical harvesting systems. The effects of skirting on fruit yields and quality in Florida are not known.
Objectives
1. Determine the effects of hedging, topping, nutritional, irrigation, and skirting treatments on the subsequent fruit yields, fruit characteristics, and conventional harvesting rates of mature hedgerow orange trees with declining production levels due to close spacing and excessive vigor.
2. Determine the effects of skirting treatments for fresh fruit purposes and mechanical harvesting on the subsequent fruit yields and fruit characteristics of hedgerow orange trees which are approximately 10 ft tall.
Summary of Accomplishments
During this fourth year, the Hamlin/Sour hedging/topping/nutrition demonstration experiment showed, for the first time, higher leaf nitrogen in 200 vs 100 lbs/acre rates (2.72 vs 2.51). No other treatment effects were evident. Treatments included hedging and topping in spring, fall, spring and fall, and spring rejuvenation hedging, and nitrogen rates of 100 and 200 lbs/acre.
In the hedging/topping/skirting experiment in 15 ft tall Valencia Rohde Red/Carrizo trees, average 1999 yields were 301 boxes/acre compared to 256 and 650 the previous 2 seasons. Subjective bloom amounts in 3/98 were significantly higher for fall as compared to spring hedging and topping. Fall topping had higher box and lb solids/acre yields than did spring topping. Trees which were re-skirted 12/98 for the first time since 10/95 removed young fruit numbers equivalent to 10-25 boxes/acre, but did not significantly reduce box/acre yields.
In the adjacent nutrition (nitrogen)/irrigation experiment in the same Valencia grove, average 1999 yields were 418 boxes/acre. Subjective bloom amounts in 3/98 were significantly higher for the low irrigation treatment (no irrigation 6/97-3/98) as compared to grower irrigation schedule year round, but the irrigation effects on 1999 yields were not significant. Nitrogen rates (130 to 220 lb/acre) affected lb solids/acre yields with the 130 and 190 lb/acre rates having the lowest and highest yields, respectively.
Manual harvesting rates for the Valencia experiments were positively correlated with box/acre yields. Compared to 1998, harvesting rates in 1999 decreased by about 30% and was related to a similar reduction in fruit size between the 2 years (123 to 181 fruit/box).
In the skirting experiment in 10-12 ft tall Valencia/Swingle trees, blossom blight was severe in the spring of 1998. The trees were re-skirted 12/98 and removed young fruit numbers equivalent to 30 boxes/acre. The trees were initially skirted 8/95 and re-skirted 6/97. In 1999, fruit yields averaged 370 boxes/acre and skirting at 36 inches reduced yields compared to no skirting. However, the cumulative four season yields (1996-1999) were very similar for all treatments (36 inch skirt, 20 inch skirt, no skirting).
Funding:FCPRAC Grants: $ 21,865
Maximum Safe Uptake of Urea N into Citrus Leaves
Project No. 981-03
Length of Project: 2 years
This report is for Year Number 1
Investigators: J.P. Syvertsen
V. Orbovic
IFAS - Lake Alfred
Abstract
Spray-induced leaf burns on citrus trees have become increasingly associated with urea sprays throughout the Florida Industry. Growers observing urea phytotoxicity frequently ask difficult questions about potential effects of application rate, temperature, humidity, and tree status on leaf burn symptoms. The primary problem is that we do not have a good understanding of leaf characteristics and environmental conditions that can limit maximum safe uptake of urea into citrus leaves. Since the thick waxy cuticle of citrus leaves is the first and most important barrier to the uptake of all foliar-applied chemicals, we will determine effects of temperature, humidity, formulation and rewetting on urea penetration through citrus leaf cuticles. We will also define effects of normal drought stress and N status on foliar uptake of urea into intact leaves in the field. Since urea has some wetting agent properties, basic information on cuticular transport will be applicable to other foliar spray materials including surfactants, plant growth regulators, abscission chemicals, N-P-K materials and pesticides. Thus, these results will have wide application to penetration rates of other foliar -applied materials used throughout the Citrus Industry.
Objectives
1. Define citrus leaf cuticle characteristics along with variations in temperature, humidity, surfactant and rewetting that will allow maximum penetration of urea through cuticles.
2. Determine effects of tree drought stress and leaf N status on maximum urea N uptake without phytotoxicity.
Summary of Accomplishments
Significant progress was made towards defining temperature and humidity conditions which would allow the highest rates of urea to safely penetrate through the cuticle of citrus leaves. Penetration of urea through the cuticle was almost complete within the first 24 hours after application. At humidities between 20-35%, penetration of urea at 28oC, was higher than at both 19oC and 38oC. Increases in average relative humidity of about 15 %, significantly enhanced urea penetration at both 28oC and 38oC. Although we expected high temperatures to increase urea penetration, urea breakdown and volatilization losses were increased by high temperature and low air humidities between 5-20%. Thus, the amount of urea diffusing through the cuticle at 38oC was lower than that at 28oC. At 19oC, urea penetration rate was relatively low immediately following urea application but due to higher air humidity at low temperatures, penetration rates were of sufficient magnitude to bring total urea penetration to the same level as that found at 28oC and 38oC four days after urea application. Addition of non-ionic surfactant X-77 to urea resulted in enhancement of urea penetration. Penetration rates were not changed, however, by adding the organosilicone surfactant L-77 to urea solutions.
Funding: FCPRAC Grants $ 43,100.
Phosphorus/Potassium Soil Test Calibration and Effects on Fresh Citrus Fruit Quality
Project No. 981-10
Length of Project: 5 years
This report is for Year Number 1
Investigator: T.A. Obreza
IFAS-Immokalee
Abstract
Phosphorus movement to surface water and nutritional effects on fruit quality emphasize judicious use of P fertilizer. Citrus response to P is rare because it usually accumulates in soil. A calibration experiment using modern soil extractants was started in 1998 in a new citrus grove that was very low in P and K. A variety of P and K fertilizer rates were applied to generate a wide range of soil-test P and K. Yield and fruit quality will be measured and related to soil tests. This research will enable the Florida citrus industry to more appropriately allocate P and K fertilizer costs, minimize impact on surface water quality, and produce higher quality fruit by understanding the main effects and interactions of P and K.
Objectives
1. Calibrate a P (and possibly
K)soil test for Florida citrus production, considering both yield and fruit quality as response variables in the calibration process.
2. Determine the main effects
and interactions of P and K fertilization on yield and fresh fruit quality of ‘Flame' grapefruit and ‘Hamlin' orange.
3. Develop fertilization recom-
mendations that will produce qualities most desired by fresh fruit consumers.
Summary of Accomplishments
In autumn 1997, about 275 trees each of Flame grapefruit and Hamlin orange were planted in the SWFREC research grove, Immokalee. In spring 1998, eighty 3-tree plots were delineated within each variety. All trees received the same rate of N fertilizer, but the plots were fertilized with four widely-varying rates of P and K to establish a range of soil test values. Soil was sampled in spring 1999 to assess the effect of applied fertilizer on soil test P and K. The soil was extracted with Mehlich 1 and Mehlich 3 solutions, which are currently used by the IFAS Extension Soil Testing Lab.
Applying P fertilizer had the desired effect of raising soil test P. While unfertilized soil had a Mehlich 1 soil test P of 3 ppm, soil receiving 50, 100, and 200 lbs/acre P2O5 had soil test P values of 8, 11, and 15, respectively. Conversely, applying K fertilizer did not significantly raise soil test K. Unfertilized soil had a Mehlich 1 soil test K of 10 ppm, while soil receiving 100, 200, and 400 lbs/acre K2O had soil test K values of 9, 10, and 8 ppm, respectively. If a nutrient does not accumulate, soil testing for that nutrient is of no value. The continued failure of K to build up in the soil will support the current practice of annually applying K fertilizer at similar rates as N fertilizer.
Funding: FCPRAC Grants $ 6,000
Gibberellic Acid and Juice Quality of Processing Oranges:Effects of Application Timing, Adjuvants and Tank Mixes
Project No. 981-12
Length of Project: 2 years
Investigator: F.S. Davies
IFAS - Gainesville
Abstract
Preliminary data suggest the application of gibberellic acid (GA) in the fall increases juice extraction weight during processing, possibly by increasing peel firmness. Even a slight (3%) increase in juice weight would be economically beneficial to growers. This study investigated the effects of GA application timing on juice weight and whether GA is still effective if tank mixed with avermectin and Aliette. In addition, possible effects of GA on return bloom and tree vigor were also studied. GA has the potential to be an important part of the citrus spray program for processing oranges.
Objectives
1. To determine the optimum time
of GA application for increasing juice extraction weight, peel firmness, and color of Hamlin, Pineapple and Valencia oranges.
2. To determine the effects of
adjuvants, avermectin and Aliette on the efficacy of GA sprays.
3. To determine if GA sprays
affect tree vigor or return bloom.
Summary of Accomplishments
Application of GA from 26 Aug. until 9 Oct. effectively delayed peel color development and increased firmness. However, the later the spray application the longer the effect persisted. The effects of GA generally persisted for 5 to 6 months after application. GA sprays also numerically increased juice extraction weight but the effect was statistically significant only on 24 Feb. for the 2 Oct. (color break) application. There was a low to moderate correlation between juice extraction weight and peel color and firmness for most application dates. However, the correlation was high for juice weight and peel firmness within a particular treatment. Therefore, it appears that GA should be applied near or after color break. The date of GA application should be based on projected harvest date. GA delayed onset of return bloom, but there appeared to be no long-term, negative effects on yields. In addition, there were no effects of avermectin, kinetic adjuvant, or Aliette on the efficacy of GA, suggesting that GA could easily be integrated into the regular citrus spray program. The timing study will be repeated using the same trees in 1999-00 to determine if there are cumulative effects of GA treatments over time.
Funding: FCPRAC Grants $ 25,000
Management of Crop Load on Alternate and Low Bearing Cultivars of Citrus
Project No. 981-16
Length of Project: 2 years
This report is for Year Number 1
Investigators: L.G. Albrigo
IFAS - Lake Alfred
E.W. Stover
IFAS - Ft. Pierce
Abstract
Enhanced control over cropping is likely to provide significantly greater profit for the fresh market citrus producer. Several methods for controlling cropping and reducing biennial bearing were examined. Reduced cropping in the "on-year" should enhance profitability by increasing fruit size and reducing limb breakage (notably in Murcott and Sunburst) and is also likely to increase bloom and cropping the following year. Reduced crop load in grapefruit is likely to be advantageous by increasing fruit size early in the season when premium prices are received. Treatments examined included Winter (usually late December) GA applications (to reduce flower initiation), postbloom hedging and topping, postbloom chemical thinning treatments, and winter urea treatments (to see if fruit size relative to cropping could be increased by increasing "bud strength"). Seedless navel and Ambersweet routinely blossom excessively but produce small crops. A number of treatments are being evaluated to see if cropping can be enhanced in these varieties. Treatments include December GA3 treatments to reduce excessive flowering, December urea to strengthen buds, and GA3 or nutrients at bloom to increase fruit set. Crop load, fruit size, fruit quality, return bloom, and grove economics were examined.
Objectives
1. Determine effectiveness of a range of techniques, alone and in combination, for controlling crop load on Florida citrus trees with the goal of enhancing production of premium sizes for fresh market sales.
2. Evaluate effect of reduced (or increased) crop load on fruit size, quality and return bloom.
3. Evaluate the economic advantages of controlling cropping in citrus trees.
Summary of Accomplishments
Citrus trees flower very heavily with as few as 0.5-2% of flowers producing fruit that are carried to harvest. Our studies in 1998-99 have demonstrated increased fruit production in navel and some Ambersweet blocks through reducing resources wasted on excessive flowering. A single GA application during the floral induction period significantly reduced flowering, and increased total production of 25 to 45% for the 98-99 season in some experiments and appears to have provided good responses through May-June drop in 99-2000. Some Ambersweet blocks did not respond again in 1999. Whether this approach will increase profitability of other Florida citrus cultivars and the most effective treatment timing need to be determined. Some citrus cultivars, especially tangerine-types, frequently set too many fruit to achieve the most desirable fruit sizes, and occasionally will result in numerous broken branches. A single NAA application to Sunburst, Murcott or Marsh in the on-year, during early fruit development, increased value by $200-3400 / acre. Thinning treatments appeared to have provided excellent results again in 99-2000. Annual hedging and topping plots were established in a mature Murcott block and reduced yields the first year. Improved fruit size did not occur across all pruned plots. While our results have been very promising, additional data are necessary for providing strong recommendations to the Florida citrus industry.
Funding: FCPRAC Grants $31,000
MANAGEMENT/PHYSIOLOGY
Completed Projects
Use of Host-specific Pathogens as Bioherbicides to Manage Weeds in Florida Citrus
Project No. 942-33
Length of Project: 4 years
Investigators: R. Charudattan
M. Singh
R.M. Sonoda
IFAS - Gainesville/
Lake Alfred/Ft.Pierce
Abstract
We have developed a bioherbicide to control several weedy grasses in citrus. The bioherbicide is a mixture of three fungi indigenous to Florida: Drechslera gigantea, Exserohilum longirostratum, and Exserohilum rostratum isolated from large crabgrass (Digitaria sanguinalis), crowfootgrass (Dactyloctenium aegyptium), and johnsongrass (Sorghum halepense), respectively. In trials conducted in a greenhouse, each pathogen (2x105 spores/ml) as well as a mixture of the pathogens (1:1:1 v/v; total 2x105 spores/ml) caused 82.5-100% disease severity on large crabgrass, crowfootgrass, johnsongrass, southern sandbur (Cenchrus echinatus), guineagrass (Panicum maximum), Texas panicum (Panicum texanum), and yellow foxtail (Setaria glauca). Fifty nontarget plant species from 11 families were either immune or resistant to each pathogen and the pathogen mixture. A biphasic culturing technique was developed to mass-produce inoculum for field studies. In separate field trials conducted in Florida (1996 and 1998), an emulsion-based inoculum of D. gigantea, E. longirostratum, and E. rostratum (5x105 spores/ml) and a mixture of these pathogens (1:1:1 v/v; total 5x105 spores/ml) almost completely killed the seven weedy grasses mentioned above and a natural population of guineagrass. The weed control lasted for 10 to 14 weeks. Thus, D. gigantea, E. longirostratum, and E. rostratum have potential to be developed as bioherbicides for the management of weedy grasses in citrus. The use of a bioherbicide mixture is a novel and effective way to control weedy grasses in citrus.
Objectives
1) Determine the nontarget host reactions to inoculation with Drechslera gigantea, Exserohilum longirostratum, and E. rostratum, and a mixture of the three bioherbicidal fungi.
2) Develop a method for inoculum production and application of the bioherbicidal agents.
3) Determine weed control efficacy of individual agents and a mixture of the three agents in mini-plot trials (repeat trials).
Summary of Accomplishments
We have developed a bioherbicide mixture consisting of three fungal pathogens indigenous to Florida, namely, Drechslera gigantea, Exserohilum longirostratum, and E. rostratum. These fungi were isolated respectively from large crabgrass, crowfootgrass, and johnsongrass. The safety and weed-control efficacy of these pathogens, singly or in a mixture, have been demonstrated in greenhouse and field trials, respectively. Fifty plant species from 11 families were not affected by the pathogens, when tested alone or as a mixture. Important crop plants in the family Poaceae, which are reportedly hosts to pathogens of the genera Drechslera and Exserohilum, were resistant to the three pathogens and the pathogen mixture. All other economically important crop plants tested were immune to all three pathogens and a mixture of the three pathogens. Also, the crop plant species tested were safe against an emulsion-based inoculum preparation of the pathogen mixture. The emulsion-based inoculum was later found to be the most effective under field conditions.
A technique for mass production and multiple harvest of these fungi was developed to produce sufficient inoculum needed for field studies. Spores of the three fungi were produced using a biphasic culturing system. The spores were viable for at least three years when stored as dry spores or in soil kept at 4oC.
The efficacy of the pathogen mixture to control several grasses was tested in the field. The pathogens were tested individually and as a mixture. During the experimental period of 14 wk, all treatments were reapplied twice (1996) and once (1998), at 2-3 wk intervals. An emulsion-based inoculum preparation (40% oil concentration, Sunspray 6E®) of the individual pathogens and a mixture of the three pathogens almost completely controlled seven weedy grasses: large crabgrass, crowfootgrass, johnsongrass, guineagrass, Texas panicum, southern sandbur, and yellow foxtail. The weed control lasted up to a period of 14 weeks without any significant regrowth. Similarly, the bioherbicidal control of a natural population of guinea grass with the pathogen mixture was field-tested (1996 and 1998). During the experimental period of 10 wk, all treatments were reapplied once at a 2-wk interval. An emulsion-based inoculum preparation of each pathogen and a mixture of pathogens almost completely controlled guineagrass in the field up to a period of 10 weeks without any significant regrowth.
Thus, we have developed a bioherbicide, a method of mass-production of the bioherbicidal fungi, and confirmed their safety to nontarget crop-plant species. The University of Florida has applied for patent protection for this bioherbicide and we are looking for an industrial partner to commercially develop and register the bioherbicide.
Funding: FCPRAC Grants $ 31,000
Modification of Nitrogen Application to Citrus to prevent Pollution of Groundwater
Project No. 942-42
Investigator: H.K. Wutscher
USDA - Orlando
Abstract
Results of the fourth and final year of the project investigating the extent of nitrate pollution of groundwater in citrus groves at five locations across the Florida Citrus belt confirmed the observations of the previous three years. The response to changes in nitrogen application and the prevalent levels of NO3-N in the surficial aquifer varied greatly from location to location. Each site seems to have a characteristic NO3-N level; increases above this level because of over application of nitrogen last about 12 months. Depth to water table is apparently a key factor that determines the levels of NO3-N found in the groundwater. With water tables in the 6 to 10 feet range NO3-N in the groundwater responded to changes in nitrogen applications, with water tables in the 20 ft range the response was small or nonexistent. Very high nitrate levels, as high as 80 ppm NO3-N, were found occasionally in Manatee County in a bedded grove underlain by a hardpan at 8 ft depth. Even there, there was little evidence that significant amounts of nitrate leave the groves in drainage water and occasional sampling of deep wells showed that nitrate penetration into the Floridan aquifer is rare and probably limited to the proximity of sink holes.
Objectives
The project was designed to determine year-around groundwater nitrate levels under citrus groves at 5 locations and how these levels respond to changes in nitrogen fertilization. Related water quality factors, pH, total dissolved solids, P, K, Na and Cl were also monitored. To assess changes in fertilization on the trees, leaf analyses were done and yield records were kept.
Summary of Accomplishments
The monthly sampling of water (7/98 - 7/99) from wells and drainage ditches showed the following: Near St. Cloud in the Eastern flatwoods (water table 6-7 ft, 2 high-N plots 190 lbs N per acre year as dry fertilizer, 2 low-N plots, with 95 lbs N, water pH 4.3-6.2), the average NO3-N concentration was 1-2 ppm in well water, 0-1 ppm in seepage water and 0 ppm in surrounding draining ditches. Valencia production in 1998/99 was 5.9 boxes/tree in the low N plots, 6.4 boxes/tree in the high N plots. Near Lake Wales on the ridge (Water table 20ft, 1 high-N plot, 243 lbs N per acre per year, 2 dry applications 7 fertigations, low-N plot, 128 lbs N, 2 dry applications 6 fertigations, water pH 5.6; 3 additional wells in a regular grove, 240 lbs/acre/year, water pH 8.0). Average NO3-N concentration in the high-N plot was 23 ppm, 15 ppm in the low-N plot, in the additional wells 8 ppm. Fruit production was 7.1 boxes/tree in the high N plot, 5.6 boxes/tree in the low N plot.
In Frostproof on the Ridge (water table 6-8 ft, low-N plot 160 lbs N/acre/year, 1 dry application, 13 fertigations, 1995-98, 5-7 ppm; intermediate N plot 215 lbs N/acre/year, 3 dry applications 15 fertigations, 1995-98 15-17 ppm NO3-N; high-N-plot 270 lbs N/acre/year, 3 dry applications 1995-98 30-34 ppm. All three plots were uniformly fertilized after October 1998 with 260 lbs N/acre/year, 2 dry applications and 4 fertigations, groundwater NO3-N averages for the last year: former low N plot 13 ppm, former intermediate plot 15 ppm, former high N plot 29 ppm. Fruit production was 403 boxes/acre in the former low N plot, 380 boxes/acre in the intermediate N block, and 335 boxes/acre in high N block.
In Manatee County one half of a 50-acre bedded block with a hardpan at 8ft received 220 lbs N/acre/year as dry fertilizer. The other half received 160 lbs N/acre/year in 3 of the 4 years of the test. In the third year, 220 lbs N were applied to the low-N plot by mistake. The water table in the high-N plot averaged 4 ft 3 in, in the low N plot 2 ft 4 in, water pH was in the 4 to 5 range. Average NO3-N in the high-N plot 59 ppm (range 21-80 ppm), in the low N plot 1 ppm (range 0-4 ppm). The difference in fertilization (or the lack of difference in year 3) is apparently not the cause of the sharp difference in NO3-N between the two halves of the grove. The higher water table created anaerobic conditions which favored denitrification; this seems to be the explanation of the effect. The high-N plot produced 378 boxes of Valencias, low-N plot 326 boxes/acre.
Both plots were fertilized equally with 225 lbs N/acre/year in Dade City because there seemed to be no need for change. The well on the upper end of the slope (and drainage from it) was nitrate-free. The well on the lower end of the slope remained well below 10 ppm NO3-N for three years, but after a change in fertilization to an all-liquid regime applied with a herbicide sprayer NO3-N ranged from 11 to 19 ppm. Water in a small creek at the bottom of the slope draining about 300 acres of citrus ranged from 2 - 7 ppm NO3-N. The average depth of the water table at the nitrate-free well was 3 ft 7 in, at the lower slope well 4 ft. Fruit production on the upper slope was 327 boxes/acre of Parson Brown, on the lower slope 282 boxes, mostly Valencias.
Funding: FCPRAC Grant $ 31,626
Effect of Adjuvants on Weed Control Efficacy of Glyphosate
Project No. 961-31
Length of Project: 3 years
Investigators: Megh Singh
IFAS - Lake Alfred
Abstract
Studies were conducted to examine the influence of various new adjuvants commercially available on physicochemical parameters, 14C-glyphosate distribution, field and green house efficacy of glyphosate. In general, it was observed that the role of adjuvants in herbicide enhancement effect is complicated and their effect is always specific to active ingredient of herbicide and surfactant, weed species and environment conditions. No one type of adjuvant functions well in all circumstances. Among the adjuvants tested Silwet L-77, Optima, Kinetic, Agri-Dex , Priowet 2001, MSO and Ammonium sulfate greatly increased glyphosate efficacy at 0.50 to 0.25 Ib/A in tested weed species.
1. To examine the influence of various adjuvants and their different types on physicochemical properties of their aqueous solutions.
2. To study the effect of various new adjuvants on glyphosate efficacy.
3. To study the effect of adjuvants on glyphosate effficacy in difficult to control weed species.
4. To select and test several promising combinations of adjuvants with glyphosate in citrus grove based on the greenhouse results.
Summary of Accomplishments
Under ideal conditions, glyphosate provides satisfactory post emergence (POST) control of many weeds. However, ideal conditions rarely exist in the field; consequently, efficacy might be greatly reduced. Surfactants are widely used to enhance the performance of POST chemicals. Non-ionic surfactants increased cuticular penetration of a.i. accepted to be the results of complex interactions between a.i., surfactant, target species and environment (Stock and Holloway 1993). Excellent progress has made during the last years and previous years of the project on the effect of adjuvants in weed control efficacy of glyphosate. Various adjuvants have been evaluated in greenhouse and laboratory experiments (enclosed list). Different representatives of broadleaf and grassy weed species were used in the experiment. Laboratory studies indicated that silicone based adjuvants had a lower surface tension and contact angle. Adjuvants reduced the surface tension and contact angle of the herbicide solution as well thereby enhancing their wetting properties. Among the adjuvants tested Silwet L-77, Optima, Kinetic, Agri-Dex , Priowet 2001, MSO and Ammonium sulfate greatly increased glyphosate efficacy at 0.50 to 0.25 Ib/A in tested weed species.
Funding: FCPRAC Grants $34,000
Effects of Foliar and Broadcast P and K on Size and Quality of Grapefruit
Project No. 961-33
Length of Project: 3 years
This report is for year Number 3
Investigator: B. J. Boman
IFAS - Fort Pierce
Abstract
A field experiment was initiated during the 1996/97 production year to investigate effects of increased N:K and N:P ratios with ground-applied fertilizers. The experiment is in bedded Marsh grapefruit on sour orange rootstock block in Martin County with 4 replicates of each of 9 N-P-K. All plots receive 120 lb per acre of N and K2O. Additional fertilizer in the form of muriate of potash and triple superphosphate is broadcast on selected plots to acheive P2O5 rates of 24, 104, or 184 lb per acre and K2O rates of 120, 224 or 328 lb per acre. The effects of the fertilization programs on the trees is evaluated by fruit yields and fruit size, shape, and juice quality factors.
A second component was added in 1997/98 production season to evaluate the effects of supplemental phosphorous and potassium foliar applications on fruit size, shape, and internal quality for fresh citrus production. Foliar sprays of calcium nitrate, potassium nitrate, and monopotassium phosphate (MKP) were compared to untreated trees in commercial grapefruit blocks. Foliar applications are made at critical times (pre-bloom, post-bloom, and summer) to determine the role of timing on fruit response. Treatment differences are measured by leaf mineral levels, yield, juice quality, peel thickness, and fruit size and shape.
Objectives
1. Determine the effects of higher rates of ground-applied P and K on the size and internal quality of grapefruit grown for the fresh market in a modern citrus production system.
2. Evaluate the effects of supplemental phosphorous and potassium foliar applications on fruit size, shape, and internal quality for fresh fruit production.
Summary of Accomplishments
During the 1998/99 season, Sunburst tangerine trees received 3 foliar applications of KNO3 (February, April, and July). Each application consisted of 25 lb/ac of KNO3 applied with 250 gal/ac of water. During the first spot pick on November 6 (spot on size 150 and larger), the trees receiving the KNO3 applications had 33% more fruit that were size 100 and larger compared to the control. During the second spot pick on November 30, there were no differences between treatments in the number of fruit in any of the sizes. On December 15, the trees were picked clean. At this time, the trees that received the KNO3 applications had slightly more size 150 and larger fruit than the control treatment. Gross returns were calculated based on the quantity of fruit and the price received by the grower on each pick date. The trees that received the KNO3 applications had a gross return of $4.95 per tree more than the control trees. This translates to an increased gross return of $600/ac based on the tree density of 181 trees/ac with 2/3 of the area in Sunburst (every 3rd bed was Orlando tangelo).
Valencia trees received 3 foliar applications during the season (February, April, and July). Fruit were picked from the plots during the last week of March. Juice samples taken on March 23 showed that none of the foliar treatments had differences in Brix:acid ratio or solids per box compared to the control treatment.
However, trees receiving MKP or KNO3 applications averaged about 25% more fruit count per tree, 29% more boxes per tree, and 21% more solids per tree in addition to having significantly more size 100 and larger fruit. Gross returns were calculated based on the solids per tree times the average price for the week of March 31 from Citrus Mutual's Market News Bulletin ($1.15 per lb). The gross returns for processing the fruit amounted to about $3.74 per tree more for both MKP or KNO3 treatments compared to the control trees. At 139 trees/ac, this amounts to increases in gross returns of about $500 per acre as a result of the foliar applications.
Funding: FCPRAC Grant $22,500
Irrigation Best Management Practices for Florida Citrus on Vulnerable Soils
Project No. 961-36
Length of Project: 3 years
This report is for Year Number 3
Investigators: L. Parsons
T. Adair Wheaton
IFAS - Lake Alfred
Abstract and Objectives
An irrigation BMP for mature citrus growing on vulnerable soils must:
Minimize water stress during flowering and fruit set
Allow moderate water stress during the winter to insure flower initiation
Provide adequate water for crop development during the rest of the year
Minimize leaching of nutrients and pesticides
Be economically viable.
Objectives included:
Determining the effect of partial coverage irrigation on root density and on water extraction rates from the wetted and non-wetted areas of the root zone
Comparing tensiometers, resistance, and capacitance probes for measuring soil water content
Developing methods to predict depth of water movement for various soils at different sites.
The rooting zone of selected trees was heavily instrumented with soil moisture sensors from which the rate of water extraction by the tree in both the wetted and non-wetted portions of the root system can be estimated. The treatments included wetting 25, 50, or 100% of the soil surface under the canopy. The overall goal was to develop reliable irrigation scheduling systems that meet the above objectives and are adaptable to a variety of citrus operations.
Summary of Accomplishments
Capacitance soil water content probes were installed under mature trees to monitor water uptake and movement at different soil depths. An experiment was set up that provided irrigation coverage for 25, 50 and 100% of the area underneath the tree canopy. Water use of citrus declines as soon as the soil water content falls below field capacity in all three irrigation coverage treatments. Water use declines 20 percent for every percent volumetric soil water content reduction. Water use by the trees was only one-tenth of the water use at field capacity by the time volumetric soil water content was reduced by 60 percent. This differs from other crops growing on better soils where water use remains fairly constant until 25 – 50% water depletion is reached. This discovery suggests water may be limiting citrus growth and production under soil water conditions previously thought to be optimal.
Soil moisture sensors and the water budget system both provide a satisfactory basis for irrigation management. A set of two 6-inch and two 12-inch tensiometers in a representative wetted area provide the minimum configuration for deciding when to irrigate, but the duration of irrigation requires knowing application rate, available soil water, rooting depth, and other factors. Most active water uptake was in the top 18 inches due to higher root densities down to that depth. This is the zone that should not be allowed to dry excessively in the spring. Water content at 2.5 and 5 ft depths changed relatively little except after heavy rainfall or prolonged dry spells.
Irrigation scheduling is based on a water budget that estimates all water supplied and removed from the grove. A computer program developed jointly with Drs. Xin and Zazueta simplifies this process, but daily inputs of rainfall, irrigation, and ET are required. The program computes irrigation duration and the interval to the next irrigation. This program is being refined and tested with irrigation data from our partial coverage experiment. Use of soil moisture sensors, water budgeting, or this program will improve irrigation efficiency, maintain production, and reduce movement of water and other materials below the root zone.
Funding:FCPRAC Grants: $37,600
Enhance Activity of Preemergence Herbicides With Adjuvants
Project No. 961-37
Length of Project: 3 Years
Investigators: Megh Singh
IFAS-Lake Alfred
Abstract
Effective preemergence herbicides like bromacil, simazine, norflurazon and diuron used for weed management in citrus are suspected to leach into groundwater because of their high soil mobility in the coarse soils of Florida. Our research to date indicated that adjuvants possesses the potential to reduce leaching of herbicides in soil. Laboratory work showed that it increased the surface tension of the herbicide solution thereby reducing the chance for preferential flow of herbicides, a mechanism suspected to promote ground water contamination. Some of the adjuvants tested increased sorption of the herbicide by the soil, which not only abates herbicide movement into water systems but also enhances its efficacy. We screened forty-five commercially available adjuvants using soil leaching columns. Our results indicated that the leaching of bromacil and simazine was not reduced significantly through the use of adjuvants. However, the adjuvants Gum Ghatti, Monazoline-T, E-17-2, E-18-5, Monazoline-O, and Emcol CC-55 were effective in reducing leaching of the herbicide norflurazon in a sandy soil. These adjuvants were further tested to determine optimum tank mix rates. We also determined that tank-mixing the adjuvants with the herbicide solution did not affect weed control, suggesting that herbicide tie-up was not a mechanism for reducing the leaching of the herbicide solution.
Objectives
1. Study the effect of certain adjuvants on the physico-chemical characteristics of solution of the preemergence herbicides: bromacil, simazine, norflurazon, and diuron.
2. Screen commercially available adjuvants to determine their efficacy to decrease leaching potential of preemergence herbicides.
3. Optimize use rate of promising adjuvants for each herbicide thereby minimizing their leaching ability while providing superior weed control.
Summary of Accomplishments
Some of the effective preemergence herbicides used in grove management have high soil mobilities. This not only results in potential ground water contamination (Shankland, 1985) but also causes decreased weed management efficacy due to dissipation of the herbicide from the weed germination zone. Herbicides like bromacil, simazine, norflurazon and diuron, which are otherwise effective for weed management should be made available to the citrus grower to keep operational costs down. Our research examined the use of adjuvants as a means to reduce leaching of these herbicides.
Funding:FCPRAC Grants $48,000
Evaluation of Wild Perennial Peanuts for Use as Cover Crops in Citrus Groves
Project No. 971-03
Length of Project: 3 years
Investigators: A.E.Kretschmer, Jr.
T.C. Wilson
J.W. Hebb*
IFAS - Ft. Pierce
*St. Lucie Co. Extension
Abstract
Field data have been obtained from two experiments with 35 accessions of wild peanuts under clean cultivated flatwoods conditions. Similarly, evaluation of plant spread, foliage density, and persistence of the same peanuts have continued in five young groves with soils varying from very sandy to moderately fine textured. Peanut harvesting of a small area in a young producing grove was completed.
Objectives
1. Evaluate 35 wild peanut accessions for best cover crop in citrus by determining persistence, rapidity of spread, foliage density, and nut production.
2. Determine the seeding rate to obtain complete plant coverage during a growing season.
3. Estimate the effectiveness of peanut competition on number of mowings and efficacy of nut harvesting.
Summary of Accomplishments
Two separate replicated evaluation experiments with 35 wild peanut accessions were completed on clean-cultivated flatwoods soils. Preliminary results are presented concerning selected data from four accessions that were chosen as typical of the four species: Arachis Kretschmeri (Pantanal), A. Pintoi (Pinto), A. stenosperma (Steno), and an unnamed species (Species). A majority of the entries were of the Pinto peanut type. Generally, all of the wild peanuts when established are very drought tolerant (= to bahiagrass), survive temporary flooding (grove furrows on flatwoods soils), are multi-branched, and are not damaged by periodic mowing. Most produce nuts. As examples: Pantanal, erect with lateral branches laying on the ground but not rooting; Pinto, prostrate with runners that produce roots from the runners as plant growth progresses; Steno, prostrate runners that do not root but are held in place by progressive formation of pegs; Species, similar in growth form to Pinto, with higher nut production.
Plant spread, nut yield, and nitrogen from planting on 16 June 1995 to harvest of a 2 by 2 foot quadrat per plot on 12 Feb. 1997 (Exp. 1), or planting in fall of 1997 to harvest of six 6-inch diameter cores per plot on 20 Oct. 1998 (Exp. 2)were:
Name Plant Spread Nut Yield Nitrogen in foliage-July 1998
inches millions/acre % lb/acre
1997 1998 1997 1998 if plant yield/acre is:
Feb Oct Feb Oct 1000 3000 5000
Pantanal 36 39 1.4 0.7 3.0 30 90 150
Pinto 60 189 1.6 0.2 3.7 37 111 185
Steno 60 106 1.8 3.8 3.2 32 96 60
Species 36 115 3.7 2.3 3.5 35 105 175
Plant spread of all but Pantanal is considered good to excellent. Slow spread of Steno in 1998 is attributed to severe damage by Sandhill cranes during the previous winter. Estimated nut production of Steno and Species were highest. All nuts from Feb.1997 were mature while only 47 to 59% of nut harvested in Oct. 1998 were mature. Thus, nut harvesting should be postponed until winter. Our mechanical harvesting occurred after Feb. to take advantage of the normal lower rainfall and warmer temperatures. For example, nuts were harvested from about one-half acre of Steno (planted to 3 double-row beds in 1995) in May of 1998 and 1999. No difficulties were encountered, and no damage to tree growth occurred. The use of a side-delivery rake to remove plant material from the harvested area had a positive effect of almost eliminating weed growth during the ensuing summer. This eliminated mowing of these beds until winter (for cold protection). In spite of its growth habit, Steno drought tolerance of emerging volunteer seedlings and mature plants was excellent. Additional plantings of Steno for commercial harvesting were made during 1998.
Funding: FCPRAC Grant $5,767
Yield Reduction of Citrus from Overcrowding-Economic Evaluation and Management Strategies
Project No. 971-52
Length of Project: 2 years
Investigators: R.P. Muraro
IFAS-Lake Alfred
T. H. Spreen
IFAS-Gainesville
F.M. Roka
IFAS-Immokalee
Abstract
At least one-half of Florida's current citrus tree inventory was planted since 1980. Much of these more recent plantings are at a higher tree density averaging 150 trees. Although groves planted at higher densities appear to mature more rapidly, there have been reports of groves experiencing substantial decreases once hedging and topping were initiated to control tree size. It is unknown if this phenomenon is widespread nor how it might be related to tree spacing, tree age, scion/rootstock combination, and management practices.
Growers have raised concerns with regard to yield declines in groves planted at higher densities and in which hedging and topping are used to control tree size. Clearly, if such yield decline is widespread, affected groves will generate smaller revenue streams. The primary purpose of this study to statistically analyze this problem with data from commercial groves.
Objectives
1. To establish the relationship between tree age, rootstock, scion, and tree spacing on per acre yields.
2. To use the information from objective #1 to improve long forecasts of citrus production in Florida.
3. To developed a computerized decision-aid to improve decision-making in the management of citrus groves planted at high densities.
Summary of Accomplishments
The review of literature and discussions with growers conducted in 1997-98 suggested that the study should focus its efforts on southwest Florida in those blocks who output is utilized in processed form. Given the depressed prices faced by grapefruit growers, it was determined that data would be collected only from orange groves. The varieties included in the survey are Hamlin and Valencia. The rootstocks included are Swingle, Carrizo, Cleopatra, Volkameriana, and Rough Lemon. With the change in focus towards processed utilization, some of the data previously collected could not be used.
At the present, data from over 100 blocks has been collected and assembled. Twenty-five growers/firms provided data. All blocks are located in southwest Florida. With time series data collected on each block, nearly 1000 observations are available for statistical estimation.
On each block, data was collected on scion/rootstock, planting date, tree densitiy, tree spacing, and soil type. If more than one type of soil was found in the block, the predominant soil is recorded. By season, data on production in boxes, juice yield, and fertilization was recorded.
Data was recorded in an Excel spreadsheet and then transformed into a SAS data set in preparation of statistical analysis. Although statistical analysis has not yet been completed, statistical equations will be developed to establish the relationship, if any exists, between the characteristics of a grove and production per acre.
Development of Decision Information Systems for Florida Citrus
Project No. 971-55
Investigators:
J.D. Martsolf,R.M. Peart, H.W. Beck,
F.S. Zazueta, J.W. Jones, J.K. Schueller,J.J. Ferguson
IFAS - Gainesville and
L. G. Albrigo, W. S. Castle,
R. P. Muraro, T. A. Wheaton
IFAS - Lake Alfred
Abstract
Making decisions about the best production practices, their timing and integration of options, has become very complex. Growers can use help-guides to effectively consider all of the options. Expert systems tied together on the basis of vegetative and fruit development stage can help to clarify and suggest timely options, provide production practices record keeping and free up time for other management decisions. Several units for the eventual integrated decision support system for citrus were developed to the stage of functioning prototypes during this first year of work.
Objectives
Develop and demonstrate a Preplant (rootstock selection) Decision System.
Develop and demonstrate a Melanose and Greasy Spot Control Decision System.
Develop a framework for the determination of timing and options among production practices in relation to citrus growth events to facilitate management decisions.
Develop a tree size and yield diagnostic system to be used as a baseline for comparing tree growth and yield.
Integrate these various applications within a user-friendly operating system.
6. Collaborate in the production of DISC CD-ROM Version 1.0 using graphics design to improve the interface.
Summary of Accomplishments
A third version of the preplant decision module for rootstock selection was developed and now soil mapping is being incorporated. The Cu Spray Scheduling System for disease control was completed with rain effects on weathering of Cu residues added. The Cu Spray Schedule Module was grower tested in the spring of 1999. A prototype for the production decision aid, based on best timing to stages of vegetative and reproductive growth was improved and converted to a Java applet to be compatible with other modules. It includes components of tree development, production practices and record keeping, is GPS-GIS compatible, and will integrate climatic effects on flowering intensity and time of bloom. Flowering data is being modeled now and should be completed for current data by Fall. This production practices prototype is ready for expanded grower testing. Several growers are cooperating in the integration of production practices, appropriate record keeping and user-friendly requirements. Data collection for the tree size and yield graphs by rootstock, scion, age and district is underway. Version 1.0 of a CD-ROM of citrus related software has been released.
Funding: FCPRAC Grants $ 35,000.00
Development of a Precision Agriculture System to Manage Florida Citrus
Project No. 981-02
Length of Project: 3 years
This report is for Year Number 1
Investigators: J. D. Whitney,
T.A. Wheaton, M. Miller and
M. Salyani, IFAS - Lake Alfred
J. K. Schueller, IFAS - Gainesville
Abstract
Although citrus growers usually manage their groves on a whole grove or block basis with uniform production inputs, considerable variability in various grove characteristics may exist. Some of the characteristics critical to management decisions are fruit yield and quality, tree size and health, soil type and fertility, leaf analysis, pest populations, water requirements, etc. Precision agriculture techniques can provide the tools which will allow grove owners to determine these characteristics in site specific areas within the grove. Using these characteristics, the grower can then make decisions on adjustments to cultural practice inputs which will increase profits, and apply the inputs in site specific areas with precision agriculture equipment. Accurate yield maps are essential for determining profits/losses in site specific areas and for determining whether changes in cultural practice inputs improve profits.
Objectives
1. Develop a system to accurately
map citrus yields using conventional harvesting methods.
2. Investigate site specific grove
characteristics which may be used to explain variability in yield maps.
Summary of Accomplishments
During this first year of funding, we assembled components of a yield mapping system in cooperation with GeoFocus, Inc., which were mounted on goat trucks and tested it in commercial harvesting operations. Even though fruit is not weighed in the grove, we evaluated 3 weighing systems on the goat truck and found the accuracy of the best systems to be within 2 to 3%, and could eventually be used as part of a yield mapping and fruit weight tallying system in the field. Labor tracking systems using bar codes and metal buttons were integrated with a GPS unit to improve the accuracy and utility of the yield mapping system. The metal buttons were more reliable in field operation than the bar code. Over 150 acres in 2 groves were yield mapped with a harvesting contractor/citrus grower. The overall system proved to be quite reliable in providing accurate yield data and tracking payroll information of the individual harvesters. In cooperation with another grower using other commercial yield monitors, we mapped the yields for a second season in a 130 acre grove to determine yield variability. Spatial variation of soil and leaf mineral content was determined from sampling the groves on a grid basis. Yield maps were combined with aerial photography, soil and topographic maps, and maps of soil and leaf mineral content to diagnose problem areas and develop management strategies for those areas. Spatial variation in yield was closely associated with changes in soil type and properties such as cation exchange capacity and soil texture. Areas of poor production may be improved by modifying irrigation and fertilizer management.
Funding: FCPRAC Grants: $ 35,000
Effect of Spray Droplet Size on Durability of Pesticide Deposits
Project No. 981 - 07
Length of Project: one year
Investigator: M. Salyani
IFAS - Lake Alfred
Abstract
Field observations of less residual pest control from some low-volume applications indicate that deposits generated by fine droplets may not last as long as those produced by larger droplets and may be more susceptible to wash-off and solar degradation. This implies that, in addition to spray coverage, composition of the pesticide residue may also be an important factor in the efficacy of pest control.
Spray solutions containing a copper compound (alone or with a surfactant) and a fluorescent dye were deposited on citrus leaves and artificial targets at different droplet size ranges. The targets were exposed to various amounts of rain or solar radiation. Samples were collected at different time intervals and spray residues were measured by colorimetric and fluorimetric methods. Copper residue recovery was the same for the upper and lower leaf surfaces and was not affected by droplet size or the length of sample storage. The rate of rain wash-off increased as droplet size decreased. Solar degradation rate was similar for droplet size range of 100-330 microns.
Objectives
1. Determine the effects of the droplet size and spray mixture on residue recovery from the upper and lower leaf surfaces.
2. Determine the effects of the droplet size on wash-off and solar degradation of fine and coarse spray deposits.
Summary of Accomplishments
Three experiments were conducted.
In the first experiment, spraymixtures containing Kocide DF (40% Cu++) alone or with 0.1% Kinetic surfactant, were applied at 1, 2, 5, and 10 µL drops to the upper and lower leaf surfaces, using a micro-dispenser. The targets were stored in a refrigerator and 6 samples of each treatment were analyzed by colorimetry at 0, 3-5, 7-10, 12-14, and 17-21 days post-treatment.
The results showed similar residue recovery rates for all treatments. The rates were not affected by the drop size, mixture surfactant, leaf surface type, and storage duration.
In the second experiment, droplet sizes ranging from 100 to 750 microns were applied to plastic card targets, using a droplet generating system. Spray mixtures contained Champ formula (37.5% cupric hydroxide). Sprayed targets were first exposed to a day of sunshine and then to 0, 0.02, 0.09, 0.12, and 0.30 inch rain. The targets were analyzed by colorimetry in 5 replications.
The amount of wash-off increased with the rain intensity. For any amount of rain, the targets made of smaller droplets were washed out at faster rates.
The percentages of wash-off for the 735, 330, 180, and 110 micron droplets were respectively 32.3, 38.9, 47.4, and 58.1% with 0.30 inch rain.
In the third experiment, spray mixture contained a fluorescent dye (Pyranine 10G) as deposition tracers. The mixtures were applied at droplet sizes (ranging from 100 to 750 microns) on plastic and acetate targets.
Sprayed targets were exposed to solar radiation and the radiation intensity was monitored by a pyranometer. Samples of the targets were collected at different time intervals to achieve 0.0, 3.4, 10.0, 18.5, and 27.0 MJ/m2 of solar energy. The maximum amount was achieved during about 8.5 hours of exposure in 2 days. Spray residues were measured by fluorometry in 5 replications. The amount of Solar degradation was quantified by the change in the sample fluorescence.
Overall, deposit degradation increased as the amount of solar radiation increased. The largest droplet size (750 micron) showed the highest amount of degradation (20.5%) but there was no difference in degradation of the other sizes (100-330 microns). Green plastic cards, simulating leaves, gave similar results to transparent acetate cards. There was no obvious trend in degradation of different dye concentrations.
Droplet distribution patterns, characterized on water-sensitive targets, showed a clear difference in coverage of different droplet sizes. While fine droplets gave more uniform deposition than the larger droplets they also appeared to be more susceptible to rain wash-off. However, there was no conclusive trend in vulnerability to solar radiation. It should be noted that the results may vary for different formulations.
Funding:FCPRAC Grants $9,000
Development and Maintenance of a Synopsis of Published Information on Key Emerging Florida Citrus Production Challenges
Project No. 981-59
Length of Project: 1 year
This report is for year number 1
Investigators: H. W. Browning
P. K. Russ
IFAS - Lake Alfred
Abstract
Availability of complete and accurate information is the key to success in reacting to emerging challenges provided by the invasion of exotic citrus pests, weeds and diseases in to Florida. The CREC library has been a resource for the Florida citrus industry for many years. This project was proposed to enable a targeted approach to collecting and organizing special topics for quick access.
Objectives
Survey the CREC collection fordocuments pertaining to exotic citrus pests.
Compile a bibliographic record of available documents and make this list available. Continue to update the listing for current information.
Check several on-line bibliographic databases and cross reference the citations to make a more complete survey of available information.
Organize the available reprints, books and photographs for retrieval.
Implement a cataloging project that improves the access for the entire CREC collection.
Summary
The resources of CREC library have been checked against bibliographic citations to determine the depth of collection to aid in the study of potential exotic citrus pests. A bibliography for the Medfly was prepared and distributed to several faculty members to show the capabilities of our existing system. The list of citations were cross referenced as to their availability in the CREC collection. Of 1450 cited titles, 300 were in the CREC serial collection. Document Delivery is being used to fill in the most relevant of the items not in the CREC holdings. In addition, the vertical files which have been cataloged since the 1960's, have many original USDA bulletins dealing with exotic pests. These were added to the electronic index to give some historical perspective to medfly information. Other topics which have been researched are:
CVC
Leafminer
Psylla
All areas of information gathering are dynamic. Citations are being generated each hour of every day. Many symposia on special topics and emerging methods are held every year. The CREC library will continue to update the bibliographic information and add to the physical collection of materials as they become available. In addition, we are planning to use a web based citation index available on our web site to allow individuals to search for bibliographic citations.
Funding: FCPRAC Grants
PATHOLOGY
Continuing Projects
Development of Methods to Manage Citrus Tristeza Virus
Project No. 928-74
Length of Project: 5 years
This is the report for year number 2
Investigators: W.O. Dawson,S. Gowda,D.J. Lewandowski
IFAS - Lake Alfred
Abstract
Diseases caused by citrus tristeza virus (CTV) are complex because control through the use of rootstocks other than sour orange increase other problems, particularly citrus blight. This is a project to restore the use of sour orange as a usable rootstock for Florida and to be prepared to protect citrus against stem pitting strains of CTV in the event that they become a problem. We have developed a genetic system that allows us to manipulate the virus to determine what components of CTV isolates are responsible for decline and stem pitting diseases. This information will allow development of "ideal" mild strains to use to cross protect existing citrus planting and new plants before resistant plants are available against decline and stem pitting diseases. This is the second year of the second phase of this project.
Objectives
Year 1 -- Assemble CTV cDNA clones into a series of full-genomic cDNAs from which infectious virus can be recreated. (completed)
Year 2 -- Development of methods to infect plants from CTV cDNA clones. We are now awaiting assays of inoculated plants.
Years 3-5 -- Determine how CTV causes disease in citrus by creating and examining hybrids between severe and mild isolates and mapping disease causing sequences.
Summary of Accomplishments
In the first phase of this project, we developed the necessary genetic systems to allow the research to develop methods to manage citrus tristeza diseases. We completed sequencing the entire genome of the major sequences of a decline CTV isolate (T-36) and a mild CTV isolate (T-30). Both have been assembled into a series of full-genomic cDNAs from which RNA transcripts can be produced in the test tube to infect protoplasts. This completes the most difficult component of our project. This now allows us to identify sequences of the virus that cause disease and cross protection. We are making sequence exchanges between severe and mild sequences in an effort to create "ideal" cross protecting strains. We are racing to have protecting isolates available to protect against any new severe isolates that begin threatening Florida citrus and to allow use of the sour orange rootstock where ever needed.
At the same time, we are characterizing the makeup of CTV populations. CTV isolates are complex mixtures of CTV-like viruses and defective RNAs. We are examining the interaction of the RNAs in causing diseases. We have accomplished all of the initial requirements to custom design cross-protecting isolates of CTV. In this phase we are attempting to make products that can be used to manage any CTV diseases that threaten Florida. The first goal is to allow the use of sour orange rootstocks, even in the presence of decline isolates of CTV.
Funding:FCPRAC Grants $ 36,576
(reflects FCPRAC requested 20% budget reduction)
Studies to Determine the Cause and Develop Strategies to Control Citrus Blight
Project No. 961-17
Length of project: 3 years
This report is for Year Number 2
Investigator: K. S. Derrick
CREC - Lake Alfred
Abstract
The goal of this project is to develop strategies to control citrus blight. Some groves are devastated by blight while others remain free of the disease for many years. This indicates that if the cause and methods of spread of blight were known procedures could be developed to maintain groves relatively free of the disease. Research will continue on the characterization of the blight protein p12, which is the protein used for the monoclonal antibody assay for blight detection. The gene that produces p12 has been isolated and sequenced. We propose to determine the effect the protein has on the expression of blight symptoms. For example, does p12 help the tree resist blight or does it induce symptoms? A complex of microorganisms can be detected in citrus trees by analysis of genomic fingerprints using PCR with arbitrary and consensus tRNA or rRNA primers. We have experiments in progress to determine if one of these microorganisms could be the cause of blight and if beneficial microorganisms are present in old-line trees making them more resistant to blight in comparison to trees from nucellar budwood.
Objectives:
1. To determine the cause of citrus blight.
2. To determine the function of the blight protein p12.
3. To develop strategies to control citrus blight.
Summary of Accomplishments
Experiments to identify microorganisms in blighted, healthy and old-line budwood trees were continued. Based on 16s RNA sequences and culture, 28 species of bacteria have been identified in extracts from roots of trees with blight. Experiments are in progress to determine if any of these bacteria are associated with blight. The experiments to determine the effect of old-line budwood on the incidence of citrus blight were continued and expanded. Studies on the function of blight associated protein p12 were continued. We have shown that p12 is similar to expansins, which are proteins involved in cell enlargement. To determine the function of p12, transgenic rootstocks (rough lemon, carrizo, sour orange and rangpur lime) and scions (Valencia and grapefruit) are being produced using the p12 gene. These plants will be evaluated to determine the effect that p12 has on tree growth and blight resistance.
Funding: FCPRAC Grant $56,822
Development of a Rapid Method to Determine The Decline Inducing Potential of Tristeza (CTV) And Other Virus-like Problems.
Project No.961-28
Length of the project: 4 years
This report is for the 3rd year.
Investigator: M. Bausher,R. Niedz,S. Garnsey
USDA-Orlando
Abstract
Some isolates of CTV causes severe decline in citrus tree scions grafted to the sour orange rootstock. The decline results from the death of the cells of the inner bark (the phloem) which carry the sugars, complex nitrogen compounds, and hormonal regulators from the leaves to the roots. How the virus kills these cells is unknown, and there are no rapid methods to measure decline potential of CTV isolates. Specific compounds produced by CTV infection are translocated to the bud union, induce cell death, and result in rapid tree decline. New methodology allows the collection of material without the artifacts created by bark harvesting and extraction utilizing only the active phloem. Findings decline markers will allow testing of new scions and rootstocks for markers to CTV decline. The specific objectives are outlined below:
Objectives
1. Determine the substance(s) translocated in phloem that cause necrosis in trees grafted on sour orange rootstocks.
2. Develop a system for rapid identification of CTV decline isolates based on quantitative assays for the phloem necrosis agents.
3. Develop a system for screening new sour orange-like rootstock candidates for tolerance to the phloem necrosis agent.
4. Develop a relatively rapid biological assay for CTV decline.
Summary of Accomplishments
1. Decline reaction in young grafted plants is more severe from field sources than in the greenhouse. Initially we set up experiments to determine the effects of low temperatures on increase of CTV decline symptoms. This may be because cold winter temperatures suppress replacement of virus-damaged phloem cells below the budunion. Our older chambers failed on two occasions and caused the loss of plants after 10 weeks of trial. These tests will be repeated this fall in the new chambers installed at the Ft. Pierce facility and find temperature conditions that optimize the decline reaction.
2. Micrografting techniques have been developed to produce test plants to test individual phloem exudate, components from other experiments. We increased the grafting reliability to 95% versus the 40% of earlier experiments.
3. Symptoms of stunting and pronounced yellowing occur on micrografted CTV infected scion on sour orange seedling rootstock within 5-7 weeks with the severe isolates T68 and T36. A visible reduction in growth also occurs with the mild strain T4 -and T55, but not with the yellowing and severe stunting that occur with the severe strain.
4. Separation, collection, and identification of individual fractions from plant extracts by capillary electrophoresis was carried out. Using this technique, samples of protein materials from CTV infected plants were sent for analysis and identification.
5. New rootstock hybrids using the micrografting technique and sour orange trifoliate hybrids are currently being tested.
6. Two biocides were developed to control contamination of in vitro micrografted citrus.
Funding: FCPRAC Grant $31,800
Development of Detection Methods For Citrus Psorosis Virus And Use of The Virus as a Vector to Express Foreign Genes in Citrus
Project Number: 971-43
Length of Project: 3 years
This report is for Year Number 1
Investigator: K. S. Derrick
CREC - Lake Alfred
Progress report for FY 98-99
Abstract
There is a need for methods for rapid indexing of citrus budwood for psorosis. Indexing for psorosis is now done by graft inoculation of citrus seedlings and observing leaf symptoms, which can be transitory and very mild. Also, there are some isolates that apparently do not induce any leaf symptoms, and bioindexing for psorosis is time consuming and subject to considerable error. Psorosis is one of the few remaining viruslike pathogens of citrus that cannot be indexed by nonbiological methods. We characterized an unusual spiral shaped virus, referred to as a spirovirus, that is associated with psorosis. We have had numerous requests from regulatory agencies and diagnostic laboratories for nonbiological methods for detecting this virus for use in citrus clean stock programs. This project is designed to meet that need. In addition, the virus associated with psorosis has some unusual properties that make it an ideal choice for use as a vector for expressing foreign genes in citrus. The most obvious advantage of using a virus vector for citrus is that foreign genes can be expressed in existing trees.
Objectives
1. To develop rapid detection methods for citrus psorosis virus (CPV).
2. To develop a virus vector for expressing foreign genes in citrus.
Summary of Accomplishments
Reliable PCR based detection methods for several isolates of the virus that causes citrus psorosis were developed in this project. In response to call outs from growers to examine citrus trees showing bark scaling we are now making assays using the PCR methods for citrus psorosis virus and by biological indexing. This has resulted in finding several strains of the psorosis virus and some additional unknown infectious agents. Efforts are being made to characterize these unknowns using procedures similar to those that were used to characterize citrus psorosis virus.
The complete sequence of the viral genome segment that encodes for the coat protein has been determined for isolate CRSV-4 and is being used to make RNA transcripts for transient expression of the green florescent protein and blight associated p12.
Funding: FCPRAC Grant for OE $20,000
Research in Support of Eradication and Control of Asiatic Citrus Canker (ACC)
Project No.: 981-29
Investigators: T. R. Gottwald
USDA - Orlando
J. H. Graham
IFAS - Lake Alfred
Length of Project: 3 years
This Report is for Year Number 1 (Year one of three)
Abstract
ACC has spread from residential Dade Co. and into Broward Co. in spite of an aggressive survey and eradication program. The new outbreaks in Manatee Co. have reemerged throughout the infected area. New outbreaks in commercial citrus in Colier and Hendry Co. areas have been traced back to the Miami infestation and are presumed to have occurred due to human movement. In spite of significant removal of trees from the core areas of infestations the inoculum has been spread repeatedly by hurricanes, tropical rainstorms, and tornadoes.
Objectives
1. Analyze survey data to predict areas most likely for future spread, for risk assessment, and for reevaluation of survey and eradication procedures.
2. Study bacterial populations on plant surfaces to determine their role in the risk of ACC recurring and test survival on wood, metal, and plastic surfaces to determine how bacteria are transported to uninfected citrus trees.
3. Develop and evaluate methods for detection and location of low incidence infections.
4. Sample infected plant material taken to local landfills to determine survival and potential for spread.
5. Sample air surrounding landfills chipping machinery for production of bacterial aerosols that might cause infection.
6. Evaluate new compounds for ACC control.
Summary of Accomplishments
A mobile containment greenhouse was moved from the Orlando USDA lab to the CCEP site at the OpaLocka airport. This laboratory establishes laboratory, greenhouse, and a base of operations for the numerous experiments we will conduct in the Miami area. Bacterial survival studies were conducted to determine the longevity and epidemiological significance of bacterial survival on plant material and inanimate objects in both shade and sun. Survival on most surfaces was 24 to 48 hours unless the surfaces were kept moist and in the shade.
Bacterial aerosols were found to be generated by chipping machinery and the debris that escaped the chipping machinery was capable of initiating disease in trap plants. Trap lines of susceptible plant material were also established radiating from a known point source of disease in one location in Miami to document spread of the bacteria resulting from meteorological events.
Studies on bacterial spread in urban Miami have determined disease gradients in Miami resulting from rainstorms. To accomplish this over 12,000 were located via differential GPS, and then all trees in the area resurveyed monthly. Spread from point sources of infection was calculated. Spread by rainstorms was documented up to 3400 feet, however, 99% of the disease spread was contained within 1900 feet of known infected source trees. This information has been provided to the CCEP, FDACS/DPI, and USDA, and has lead to a 1900-ft recommendation by the Citrus Canker Task Force for removal of exposed trees subject to risk assessment.
Funding:FCPRAC Grants: $ 34,057
PATHOLOGY
Completed Projects
Determination of Inoculum Levels and Environmental Factors To Predict Severity and Improve Control of Fungal Diseases of Citrus Fruit and Foliage
Project No. 961-04
Length of Project: 3 years
Investigators: L. W. Timmer, J. H. Graham
IFAS-Lake Alfred
T. R. Gottwald
USDA-Orlando
Abstract
Fungal diseases of fruit and foliage reduce yields and the external quality of fresh market fruit. We proposed to develop methods to assess inoculum levels for greasy spot, Alternaria brown spot, Phytophthora brown rot, citrus scab, and melanose prior to the infection period to determine the potential for disease development. The effect of environment on spore production, spore release and dispersal, and infection of the plant are being determined. These data will be used to develop predictive models for disease incidence and severity. This information will be useful in modifying cultural practices to reduce disease severity and as a basis to eliminate unnecessary fungicide applications and to improve the timing and effectiveness of applications made.
Objectives
1. Develop methods to quantify inoculum levels and determine the conditions under which inoculum is produced.
2. Determine the environmental conditions under which spores are released and dispersed.
3. Determine the environmental conditions necessary for infection and disease development.
4. Develop models which incorporate environmental factors and inoculum level to predict disease and determine the need for and proper timing of fungicide applications and develop cultural methods to reduce inoculum production and improve disease control.
Summary of Accomplishments
With greasy spot, infection of trap plants, leaf litter, ascospore production and weather were monitored in Lake Alfred (LA) and Immokalee (IM) from Jan 97-Dec 99. Some infection of trap plants occurred year round in LA and IM with the lowest amounts in Feb-Apr and Aug-Oct. Leaf litter and ascospore production were greatest from Feb-Jun with earlier ascospore production in IM. Winter temperatures were higher in IM promoting more rapid greasy spot development.
With Alternaria brown spot, a laboratory model to predict infection based on temperature and leaf wetness has been developed. Infection of trap plants placed in the field weekly demonstrated seasonal patterns but was of little value for disease prediction. Trap plants placed in the field daily demonstrated that most infection occurred on days with rain, >10 hr leaf wetness, and temperatures from 68-83 F. Significant infection occurred on days without rainfall if leaf wetness was >10 hr per day and temperatures were 68-83 F.
With Phytophthora brown rot, the optimum temperature for infection of fruit was 80-86 F and less than 3 hr of wetness were needed. In contrast, the optimum temperature for sporangium production was 70-75 F. Up to 24-36 hr were needed for optimum sporangium production.
Twigs affected by melanose were cut each month and suspended in mesh bags in the tree canopy. Dead twigs began to produce spores in 2-3 months and continued to produce for 8-10 months depending on temperature and rainfall.
Funding: FCPRAC Grants: $49,000
Studies on a Virus Isolated from Trees with Citrus Blight
Project No. 961-18
Length of Project: 3 years
Investigator: R. H. Brlansky
IFAS - Lake Alfred
Abstract
Citrus blight is one of the most economically important diseases of Florida citrus. The cause of blight appears to be caused by a graft transmissible agent. The identity of the agent is essential since control measures will ultimately depend on the detection of the pathogen in diseased citrus materials. We have been studying a virus isolated from blight-affected trees. We have prepared antibodies to the virus and designed a detection system. The virus has been inoculated to healthy trees and detected from them. The specific objectives of this project are listed below.
Objectives
1) Continue isolation of the virus from blighted trees and characterize it.(Year 1, 2)
2) Prepare and test antibodies for detection from blight-affected trees Accumulate detection data to determine if a relationship exists between the presence of this virus and citrus blight. (Year 1,2,3).
3) Prepare cDNA probes, sequence the viral nucleic acid and develop a PCR detection procedure. Compare the PCR data with the serological detection data for efficacy and sensitivity and correlate with the blight protein test. (Year 1,2,3)
4) Inoculate citrus trees to determine if this is the cause of citrus blight. Continue to test other plants as alternative hosts. (Year 1, 2).
Summary of Accomplishments
During the third year of this project we have continued successfully isolating and detecting the described virus from blight-affected trees. Successful isolations have been accomplished from roots and shoots of blighted trees. The virus titer was found to be lower in hotter months. The virus was successfully used to make antibodies in rabbits. Antibodies are useful for detection of viruses in plants. The antibodies were specific for the virus (did not react to citrus tristeza virus or other viruses). An ELISA test similar to that used for the detection of CTV was developed to detect this virus in diseased trees. We also detected the virus in some healthy appearing trees that tested negatively for most blight diagnostic assays. Some of these trees have recently developed blight symptoms. We continued observations and tesing of field trees for the virus.
More inoculation tests with the virus were done this year using healthy 3 ½-4 year old Hamlin/Rough lemon trees. The Hamlin/Carrizo trees inoculated previously continue to die back, flush and then die back again. Dieback similar to that on field trees occurs on flush that is produced after the trees are trimmed. These inoculated trees tested positively with the ELISA test for the virus. The results from this work generated data on the identification of the virus and developed methods to detect it. We are still determining its relationship to the cause of citrus blight. The key to controlling citrus blight is identification of the causal agent.
Funding:FCPRAC Grant: $39,700
Mild Strain Cross Protection to Protect Against Citrus Tristeza Virus for Florida Citrus
Project No. 961-47
Length of Project: 3 Years
Investigator: R.F. Lee
IFAS-Lake Alfred
Year 3 of 3-year Project
Abstract
Mild strain cross protection (MSCP)is defined as the ability of a mild strain of a virus to prevent the expression of a second, more severe strain of the same virus in the same plant. MSCP will be an important management strategy for tristeza (CTV) now that the brown citrus aphid (BrCA) is in Florida. The overall objective of this project is to improve MSCP for citrus in Florida. The interactions of CTV "populations" and strain interactions between protecting and non-protecting strains will be studied. A concentrated effort will be made to improve MSCP in grapefruit. Information developed from this project should enable better application of MSCP for control of CTV and permit quicker selection of mild strains for use for MSCP against new severe, stem pitting strains of CTV which will arise and spread in Florida in the next decade due to the presence of the BrCA.
Objectives
1. Determine the role of CTV "populations" in mild strain cross protection (MSCP). Define the population variation within severe strains of CTV which can cause damage and mild strains used for cross protection.
2. Study strain interactions between cross protecting mild strains, non-cross protecting mild strains, and severe challenge strains of CTV.
3. Continue to characterize, screen and evaluate additional mild strains of CTV for MSCP with emphasis on mild strains for use in grapefruit.
Summary of Accomplishments
Mild strain cross protection (MSCP) will become an increasingly important in Florida as a component of an integrated program to maintain citrus production in the presence of citrus tristeza virus (CTV) and the brown citrus aphid (BrCA). Progress made on this project includes development of methods useful to enable quicker selection of CTV strains having potential for MSCP; gaining knowledge about strain interactions between cross protecting and severe strains of CTV; development of a better understanding of strain diversity present in field isolates of CTV and how these strains may be separated with single aphid transmissions using BrCA; and the selection of seven "new" isolates of CTV from surviving trees which appear to have potential for MSCP in Florida. These selected isolates are undergoing replicated greenhouse evaluations to determine their performance against severe Florida strains, including grapefruit stem pitting strains, and in Beltsville, MD, for evaluation against exotic stem pitting strains of CTV. Single aphid transmissions from field collected CTV isolates indicate that field isolates are composed on a mixture of different CTV strains. Data collected suggests that rootstock usage may influence efficiency of MSCP, with selections expressing the CTV immunity gene being more effective at MSCP against stem pitting strains of CTV. In addition to selection of additional CTV mild strains for MSCP on grapefruit, this project has enabled the evaluation of field experiments whereby mild strains for cross protection were inoculated into mature sweet orange and grapefruit trees in the field. Seventy eight percent of the original trees on sour orange rootstock are remaining in the oldest field experiment (established 8 yrs ago) compared to 22 percent of the original trees in the control block where no mild CTV was introduced.
Funding: FCPRAC Grants $56,000
Evaluation of Decline and Stunting Problems in Citrus Trees on Swingle Rootstocks
Project No. 971-11
Length of Project: 2 years
This report is for year 2
Investigators: S. M. Garnsey, H. K. Wutscher , K. D. Bowman
USDA - Orlando
Abstract
Growers continue to report a variety of emerging problems in citrus trees propagated on Swingle citrumelo. These problems include tree decline and tree stunting syndromes and may involve multiple causes. The objectives of this project were to systematically investigate the possible causes of stunting and decline syndromes in trees on Swingle and determine if these problems are associated with virus or viruslike pathogens or have non-infectious causes. The information developed will help growers evaluate and control future problems on Swingle, the most commonly used citrus rootstock in Florida. FCPRAC funding provide the extra technical help and supplies needed by ARS investigators to conduct this investigation.
Specific Objectives
1. Determine location, extent, and distribution of trees on Swingle with stunting or decline problems.
2. Determine associations with specific soil conditions, use of off-type or misidentified rootstocks, use of specific cultivars or specific budwood sources.
3. Determine if a graft-transmissible agent is involved and look for evidence that new virus and virus- like pathogens may be associated with either the stunting or decline syndromes in Swingle.
4. Determine more precisely the effects of known viruses and viroids on trees grafted on Swingle rootstocks.
Summary of Accomplishments
Additional sites with disease problems on Swingle, including several on the East Coast, were visited. Indexing tests for virus and viroid pathogens failed to associate any specific syndrome with a virus or viroid infection. Observations of Roble sweet orange trees on Swingle revealed a sectorial occurrence of budunion incompatibility in early stages. A planting of Roble on 18 different rootstocks at Dundee was examined. Susceptibility to budunion incompatibility varied among trifoliate hybrids, and even among different citrumelos. This indicates that incompatibility is a segregating trait. A test was established at Immokalee to determine if a new bark scaling problem affecting grapefruit trees on various rootstocks, including Swingle, is graft-transmissible. No evidence for transmission was seen after 1 yr. in young trees. RAPD markers were developed that can distinguish citrumelos from other trifoliate hybrids and separate zygotic and nucellar seedlings within cultivars. Further development of markers to differentiate individual citrumelos is feasible. Completion of field plot facilities for the new ARS laboratory at Ft. Pierce were delayed. This precluded establishment of field plots to test for transmission of the various syndromes affecting trees on Swingle and testing effects of known viruses and viroids on Swingle.
Funding: FCPRAC Grant $4,000
Attempt to Genetically Engineer Grapefruit for Resistance to Citrus Canker Disease
Project No: 981-18
Length of project: 1 year
Investigator: D.W. Gabriel
IFAS - Gainesville
Abstract
Asiatic citrus canker disease continues to spread in Miami, despite an intensive eradication program. There is a constant threat of canker spread by hurricane or by man to commercial groves. Other than eradication, there is no known effective control. Basic research in my UF lab over the last 14 years has revealed the mechanism by which the pathogen causes the disease, and with this knowledge has come several strategies that might work in genetically engineered citrus to block the pathogenicity mechanism. One such strategy involves protein "aptamers", which have been selected to bind functional areas of a pathogen protein, PthA, that is critical for canker development. PthA is literally injected by the pathogen into citrus cells to cause the disease symptoms. The sole specific objective is stated below.
Objective
1. Use transient expression assays in citrus to determine which aptamers, if any, are effective in blocking the activity of PthA to cause cankers on citrus.
Summary of Accomplishments
Two aptamers were identified that provided sufficient blocking activity on citrus to warrant immediate efforts to transform citrus. We first developed two (recently published) assays that were used to cause cankers on citrus in the absence of the citrus canker pathogen. We then used these assays to evaluate aptamers that appeared to bind to the pathogenicity protein PthA to determine if they would block the function of PthA and eliminate the cankers. As a result of this work, the University of Florida has filed a "continuation in part" (CIP) of its patent on the use of aptamers to control disease, and USDA-APHIS has provided follow-on funds through the SBIR program to Integrated Plant Genetics, Inc. to genetically engineer citrus to determine if these aptamers can provide meaningful genetic resistance to Asiatic Citrus Canker disease.
Funding: FCPRAC Grants $24,000
Postinfectional Activity of Systemic Fungicides for Control of Citrus Scab and Melanose
Project No. 981-20
Length of Project: 1 year
Investigators: L. W. Timmer
IFAS - Lake Alfred
Abstract
Citrus scab and melanose seriously reduce the quality of fresh fruit. Preventive fungicide applications can provide acceptable control if properly timed, but unexpected rains can produce serious damage. The systemic fungicides, benomyl, fenbuconazole and a strobilurin, will be evaluated for postinfectional activity against scab and melanose. Susceptible seedlings such as grapefruit or rough lemon will be inoculated with Elsinoe fawcettii or Diaporthe citri and then sprayed with commercial rates at different times up to 96 hr after inoculation. Symptom severity will be evaluated after 10 days. If the approach appears feasible, additional fungicides will be evaluated. If the technique is successful on inoculated seedlings, postinfectional applications will be evaluated in the field the second year.
Objectives
1. To evaluate the postinfectional activity of a benzimidazole, a sterol-biosynthesis inhibiting fungicide and a strobilurin against melanose and scab on citrus seedlings in the greenhouse.
2. To ascertain the potential for postinfectional sprays in the field using the most effective treatments from greenhouse studies.
Summary of Accomplishments
Benlate (benomyl) and Abound (azoxystrobin) showed postinfectional activity against citrus scab. Fungicide application up to 72 hr after inoculation reduced the amount of infection, but these products would need to be applied within 48 hr for good control. Fenbuconazole (Enable) showed little postinfectional activity against scab. With melanose, Benlate and Abound showed some limited activity, but Enable did not appear to be effective. Postinfectional control of melanose in the field does not appear to be feasible with current products.
Funding:FCRAC Grants: $ 10,000
Biological Diversity of Citrus Tristeza Virus
Project No. 981-22
Investigator: C.A. Powell
IFAS-Ft. Pierce
Abstract
Citrus tristeza virus (CTV) is not a single virus but a family of related viruses. It has been known for many years that buds from different trees infected with CTV give rise to a variety of symptoms when used to inoculate indicator plants. Immunological and nucleic acid analysis have confirmed field and greenhouse observations that not only is CTV a diverse entity but the different CTVs frequently occur in mixtures. Preliminary results in Fort Pierce and Orlando had suggested that some so-called mild CTV isolates contain a severe component and so-called severe isolates contain a mild component. These components can be separated by passage through different varieties of citrus. This proposal uses established methods to inoculate several citrus indicator varieties with several mild isolates of CTV including those that may have cross-protecting potential. Analysis of the indicators reveals that some of these mild isolates contain masked severe isolates that are expressed in some citrus varieties. Some budwood sources that contain mild isolates may pose a danger to the citrus industry.
Objective
Examine mild isolates of CTV that have potential use in cross-protection for severe components of CTV.
Summary of Accomplishments
Budwood was collected from sweet orange trees from commercial groves that were positive for CTV using MAb 17G11 (reacts with most Florida isolated CTV) and negative for CTV using Mab MCA13 (reacts with severe but not mild isolates of CTV), and used to inoculate Mexican lime, Madams Vinous, Hamlin on sour orange, and Duncan grapefruit indicators. Three percent of the Madam Vinous and 40% of the Duncan grapefruit became MCA 13 positive. All the Mexican lime and Hamlin on sour trees remained MCA13 negative. A severe isolate of CTV was also recovered from MCA 13 negative stock plants containing the T4 and T30 isolates of CTV by bud inoculation to Duncan grapefruit and Madam Vinous, respectively. These data indicate that both commercial citrus and greenhouse maintained stock plants with mild CTV isolates may also contain severe isolates of CTV that are not detectable by ELISA but can become detectable when transferred into other citrus hosts.
Funding:FCPRAC Grant $10,000
Development of a New Generation of Marketable Probes with Increased Sensitivity And Speed for the Detection of Specific Strains of Citrus Tristeza Virus.
Project No. 981-25
Length of Project: 2 years (terminated after year 1).
This report is for year Number 1
Investigators: C. L. Niblett
IFAS - Gainesville
R. F. Lee
IFAS - Lake Alfred
Abstract
The overall objective of this research was to develop fluorogenic probes capable of rapidly and accurately detecting and differentiating specific strains of citrus tristeza virus (CTV). We have succeeded in the primary portion of that objective and greatly enhanced the sensitivity of CTV detection in large composite samples of potentially infected citrus trees. We also have developed a sensitive method for detecting minor components of CTV populations.
Objectives
1. Prepare fluorogenic probes equivalent to the current strain specific probes for CTV.
2. Develop fluorogenic probes for unique severe or useful mild strains of CTV.3.Increase the sensitivity and speed with the fluorogenic probes to simultaneously detect several strains of CTV in single or large composite samples of citrus trees.
4. Conduct demonstration and training sessions in the use of the probes.
Summary of Accomplishments
We made excellent progress during Year 1 and are unclear why funding was terminated. Two new probes capable of differentiating quick decline and mild strains of CTV were developed. Fluorogenic technology enabled us to enhance the sensitivity of detection to 1 infected tree in 1000, much greater sensitivity than was anticipated. It will facilitate the Florida Quality Tree Program in the necessary testing of large numbers of trees. We also developed a new and sensitive method for detecting low populations of CTV strains in mixed infections. This is important because low populations of severe strains may have major biological implications and must be detected and eliminated from the budwood stream before wide distribution by the brown citrus aphid. We have detected of up to four CTV strains infecting the same tree. Our new approach, confirmed by sequencing, is more sensitive than previous approaches, having the added advantage of providing clones of minor populations for characterization and elucidation of the diversity of CTV.
Funding:FCPRAC Grants $52,000
Control of Citrus Blight by Cross Protection with Benign Strains of Xylella fastidiosa
Project No. 981-28
Length of Project: 2 years
This report is for Year Number __1__
Investigator: D.L. Hopkins
IFAS - Leesburg
Abstract
Citrus blight, present in Florida citrus groves for more than 100 yrs, continues to be a serious production problem resulting in annual losses of up to 500,000 trees per year with an estimated loss to growers of $52 million. Injection of trees with benign strains of Xylella fastidiosa reduced blight incidence. This proposal investigates cross protection against citrus blight by benign strains of X. fastidiosa in mature trees in the grove, comparing one-time injection with multiple injections with benign strains for control of blight in the grove and identifying more-effective biological control strains of X. fastidiosa. A method of injecting citrus trees for the control of blight that would reduce the yearly loss to citrus blight should result from this work. Specific objectives are outlined below.
Objectives
1. To evaluate the control of citrus blight with twice yearly injections of the scion and rootstock with different strains of X. fastidiosa.
2. To evaluate one-time injection versus multiple injections of trees with benign strains of X. fastidiosa for control of blight in the grove.
3. To identify new, more effective, benign strains of by their ability to systemically colonize young citrus trees in the greenhouse.
Summary of Accomplishments
To compare single injection with multiple injection of X. fastidiosa strain Syc86-1, seven treatments of 40 trees each were established in a grove in St. Cloud. Treatments were: 1) a single injection in the scion and rootstock in October 1998; 2) a single injection in the scion and rootstock in April 1999; 3) injections in the scion and rootstock at 6-month intervals; 4) injections in the scion only at 6-month intervals; 5) injections in the scion only at 18-month intervals; 6) injections in the rootstock only at 18-month intervals; and 7) untreated control. All treatments except treatment 2 were initiated the last 2 weeks of October 1998. This experiment needs to be continued for 4 to 5 years to determine whether a single injection is as effective as multiple injections. During this fiscal year, all of the trees that have not developed blight after 4 yrs in the twice-yearly injection experiment were re-injected with benign strains of X. fastidiosa or buffer. Four of the 5 benign strains of X. fastidiosa continued to reduce the development of citrus blight by 14 to 43%. While this level of control of blight is not ideal, it is sufficient to be economically significant. Seventy-five percent of the trees still producing after 4 yrs is certainly better than 50% producing. This experiment will be evaluated for another year, or two.
Funding:FCPRAC Grants $22,000
ENTOMOLOGY
Continuing Projects
Biological and Chemical Controls for Diaprepes abbreviatus Larvae and Adults
Project No. 942-18
Length of project: 3 years
Investigators: C.W. McCoy, D.I. Shapiro,L.W. Duncan
IFAS-Lake Alfred
Progress Report for FY 98-99, year 2 of 3rd year
Objectives
Tree decline maladies are common to Florida citrus; however, their importance can be exacerbated by larval injury to roots caused by Diaprepes and other citrus root weevils. Independently, larval injury to the structural roots by Diaprepes also can cause severe tree decline and mortality. Short-term control of the larvae, before root injury occurs, appears to be the best strategy for minimizing root injury by insects and disease. To accomplish this objective, treatment of the soil surface to form a barrier or treatment of the tree rhizosphere is required. A number of biological and chemical agents have been tested both as a barrier treatment and as a total root treatment. Previous research suggests the fungus Beauveria, though infectious with and without a chemical synergist, has a very short persistence on the soil and is ineffective as a barrier treatment. The chemical agent bifenthrin, has better persistence (8-12 wk) at the soil surface, but lose residual effect quicker during the summer. Nematodes give short-term control and are ideal for use in early summer and fall. A soil fumigant, sodium tetrathiocarbonate, is effective against all larval ages in the greenhouse studies. Each control agent is unique and performance can vary. Questions on field efficacy and non-target effects remain to be examined. Our research objective is to continue research on developing cost effective ways to larval control strategies in ridge and flatwoods soils and to evaluate different sampling methods for assessing larval control. Particular emphasis is being given to optimizing the use of nematodes as a larval control.
Summary of Accomplishments
Brigade insecticide is available under a Section 18 Exemption for use for control of Diaprepes in citrus groves. When applied to the soil beneath the tree, where leaf litter is minimal, research showed up to 12 wk residual control from 85-95% during April through mid-June, 1998. Trials conducted in September gave 6-8 wk residual control. At 5 lb form/A, Brigade was effective against neonates and reduced fire ant populations. The reduction in fire ants by Brigade resulted in an increase in other predatory ants that also attack Diaprepes larvae. Although fire ants are also predatory, it is generally accepted, that a complex of ant species is more favorable than one or two dominant species.
Sodium tetrathiocarbonate, a soil fumigant was effective as a soil drench to container grown grapefruit at 500 and 1000 ppm. It killed 88.2 and 94.3% of the larvae feeding on the root to a depth of 12 in within 72 hr.
The nematodes, Steinernema riobrave, Heterorhabditis bacteriophora and H. indica were field tested at different rates as aqueous or clay formulations. Nematodes were applied in June and September using herbicide delivery at 100 gal/A in a flatwood grove. Rates of 50,000 nematodes/ft2 or greater were required to achieve significant larval infection in Diaprepes. Larval infection was not influenced by nematode species. When nematode rate was less than 50,000/ft2, larval mortality was caused by ant predation, nematode, fungal and bacterial infection in descending order of importance. When the nematode rate was greater than or equal to 50,000/ft2, nematode effect was greater than or equal to the ant effect.
Effects of temperature and host age on nematodes infectious to Diaprepes were tested in the laboratory. Virulence and reproductive potential were compared among the nematodes: Steinernema riobrave, Heterorhabditis bacteriophora, and H. indica. Older larvae were less susceptible to nematode infection than younger larvae. Nematodes were less virulent at 21 C than at 24 C or 27 C. Virulence of H. indica was greater than H. bacteriophora in 50-d-old Diaprepes larvae at all temperatures, and greater than the other two nematodes in 20-d-old larvae at 24 C. Heterorhabditis bacteriophora was more virulent than S. riobrave in 20-d-old larvae at 24 C, whereas S. riobrave was more virulent than H. bacteriophora at 21 C (in 50-d-old larvae). Reproductive potential was greatest in H. indica followed by H. bacteriophora.
Funding: FCPRAC Grants: $ 42,678
Suppression of Caribfly Egg-Laying
Project No. 971-12
Length of project: 2 years
Investigators: H. N. Nigg
IFAS - Lake Alfred
S.E. Simpson
FDACS-Winter Haven
Abstract
For many Florida citrus growers the control of fruit flies (Caribbean fruit fly) is a major task that involves the application of a bait plus an approved insecticide. This proposal investigates the suppression of egg laying of females treated with selected insecticides. This action interrupts the egg laying in fruit and provides the grower with increased yields and improved fruit quality. This project will provide pesticides which are alternatives to malathion.
Objectives
Fruitflies, including Caribbean fruitfly, are controlled through application of a bait plus insecticide. In Florida the suppression of Caribbean fruitfly populations is part of the fly-free zone for export of grapefruit, particularly to Japan. Insecticide applications are designed for absolute kill of the adult population.
Since the life stage which damages fruit and results in quarantine and spray programs is the larva, this research program is directed to interrupting laying of eggs in fruit.
In the initial experiments, flies obtained from DPI, Gainesville, as pupae will be allowed to emerge as adults and then split into cages. These flies will be treated with insecticides to determine the LC50 (oral dosing) and if, when and for how long egg laying stops. Flies will be treated at about six days old. Egg laying and egg viability will be assessed before dosing. When egg laying resumes, eggs will be checked for viability.
Those insecticides which suppress egg laying or result in nonviable eggs will be combined with the commercial lure NuLure and the attractiveness of the insecticide-bait tested.
The results from these tests will be used in the development of a large cage, Calomondin-based bioassay to determine if egg laying remains suppressed in the presence of suitable fruit.
The overall objectives of these experiments is to provide technology for field testing.
1) To determine the LC50s of registered pesticides not subject to previous testing on a Caribbean fruitfly.
2) To determine the effective dose of insecticides for egg laying suppression.
3) To determine egg viability before dosing and after egg laying resumes.
4) To develop a fruit bioassay for egg-laying suppression and viability.
Summary of Accomplishments
This has been a highly successful project. Thirty pesticides have been screened at 100 ppm for kill and egg-laying suppression. Fifteen of these killed over 80% of the flies at 100 ppm. All 15 have been assayed at 10, 20, 30, 40 and 50 ppm to determine an LC50. Three of these active pesticides suppressed the egg-laying in A. suspensa at below 50 ppm. For three pesticides we were able to calculate an LC50 at 10-50 ppm. Eleven pesticides were too toxic to calculate an LC50 at 10-50 ppm. The doses for these are being adjusted downward and the LC50s are being redetermined.
This project has suggested a minimum of 14 replacements for malathion, the current bait spray pesticide for fly-free zones. Four of these replacements are organophosphates and may not be approved. Eight compounds are natural products and stand an excellent chance of approval for eradication programs and for fly-free zones. It is evident that malathion can be replaced by pesticides which we have tested and at doses at least 2000X less than the recommended rate for malathion.
This project developed a greenhouse testing method for pesticides to screen pesticides before expensive field tests.
Funding: FCPRAC Grants: $ 22,000
Suppression of Egg Laying of Diaprepes abbreviatus
Project No. 971-14
Length of project: 2 years
Investigators: H. N. Nigg
IFAS - Lake Alfred
S.E. Simpson
FDACS-Winter Haven
Abstract
The Diaprepes root weevil is an important long-range pest for many Florida citrus growers. Presently, there is a limited number of approved pesticides which can be used for control. This proposal investigates registered pesticides for their ability to kill and to suppress egg laying in D. abbreviatus. Control efficiencies could result in lowered adult populations and increased yield from infested citrus groves.
Objectives
This project is investigating the suppression of egg laying and death of field-collected D. abbreviatus by ingestion of pesticides. Females which are laying eggs are fed citrus foliage to which candidate chemicals have been applied. The number of egg masses and their viability are monitored before and after insecticide consumption.
We expect to find chemicals which interrupt egg laying and to determine the length of time they have that effect.
The difficulty with D. abbreviatus is that the larva is the damaging life stage. It is inaccessible to many control measures because it feeds on roots. The damage and population of adults is normally not noticed until the grove is infested. Micromite® currently is recommended for suppression of egg laying and the production of non-viable eggs. Due to the variable and long life cycle of D. abbreviatus, it is difficult to assess the effect of Micromite® (or any other control measure) on the population of D. abbreviatus and these assessments are better conducted in the laboratory initially.
The objective of this study is to evaluate registered pesticides for their ability to kill and to suppress egg laying in D. abbreviatus.
Summary of Accomplishments
This project is on track and is successful. We have determined the egg laying pattern (number of egg masses, number of eggs/mass, time between masses, and egg production over the life span) of five Florida D. abbreviatus populations. We have determined by PCR-RAPD and by esterase analyses the relationships between 6 Florida D. abbreviatus populations. These data were then used for testing 31 insecticides for their ability to kill D. abbreviatus with a 100 ppm oral dose. This testing was further refined by using oral doses of 10, 20, 30, 40, and 50 ppm active ingredient to determine an LC50 and to determine if egg laying was suppressed in females.
We have tested all 31 insecticides at 100 ppm. Of these 31 insecticides, only 2 (fipronil and Rhône-Poulenc EXP 61685B) killed 100% of Diaprepes adults. We now have tested 11 pesticides in the 10-50 ppm phase of these experiments. Five of these pesticides reduced egg laying with LC50s of about 30 ppm.
The PCR-RAPD data indicated that the Orlando laboratory population was physiologically the most homogeneous. The South Port population was the most homogeneous genetically.
In the egg laying pattern experiment the Orlando population laid twice as many eggs as other populations; South Port laid the least number.
We have completed a fipronil soil incorporation experiment with citrus seedlings and Diaprepes larvae. 25 ppm fipronil incorporated into soil provided 100% control of Diaprepes larvae over 90 days.
Funding: FCPRAC Grants $ 9,500
Classical Biological Control of Citrus Psylla and Pink Mealybug
Project No. 971-21
Length of Project: 4 years
This report is for Year Number 1.5
Investigators: M.A. Hoy
IFAS - Gainesville
Ru Nguyen
FDACS - Gainesville
Abstract
This project originally was proposed as a "proactive" classical biological control program for two pests that were expected to invade Florida. We expected the pink mealybug to invade Florida first because it was already found in multiple Caribbean islands. Surprisingly, the Asian citrus psyllid invaded Florida first and was discovered in June 1998. By June 1999, Asian citrus psylla has been found in at least 12 counties in Florida. We imported two parasitoid species that attack the Asian citrus psyllid from Taiwan and Viet Nam in November 1998. We have evaluated both species and submitted our application in June 1999 to state and federal regulatory authorities to release the first species (Tamarixiaradiata). Approval was obtained and the first releases of T. radiata took place near Fort Pierce and Indiantown on July 15, 1999. We hope to obtain permission to release the second parasitoid species during the 1999 growing season. We want to discover the pink mealybug while it is still in a relatively small area in Florida so that we can release parasitoids immediately, thereby reducing the damage it can cause.
Objectives
1. Obtain permits to import parasitoids of the citrus psylla and the pink hibiscus mealybug.
2. Obtain host plants and develop rearing methods for both pests and their parasitoids.
3. Obtain parasitoids and evaluate them in quarantine; write environmental assessments.
4. Obtain permits from state and federal regulatory agencies to release them in Florida.
5. Mass rear and release parasitoids in Florida citrus groves.
6. Evaluate overwintering, dispersal, and impact of parasitoids on pests.
Summary of Accomplishments
When this proposal was written, neither the citrus psylla or the pink mealybug were present in Florida, but both were the targets of classical biological control programs because effective natural enemies are known for both. This project officially began January 1, 1998.
The Asian citrus psylla was found in southeast Florida in June 1998, and our "proactive" classical biocontrol project was off and running! We have identified sources of parasitoids of the psylla in Taiwan, Thailand, and Viet Nam. We have permits to import them, purchased 2400 citrus jessamine plants (Murraya paniculata) for rearing psyllids in quarantine and built cages. We obtained permits to bring psyllids from southeastern Florida to Gainesville to rear them in quarantine as hosts of the parasitoids. We developed a molecular test (polymerase chain reaction) to confirm the absence of greening disease in the psyllid colony and in the parasitoids imported from Asia.
We obtained the assistance of taxonomists at the British National Museum who have confirmed the parasitoids' identity (for a fee). We obtained shipments of parasitoids from Taiwan and Viet Nam in November 1998 and have reimbursed the cooperators for their costs.
We have developed a rearing program and carried out evaluation in quarantine of the host range of T. radiata. We expect to produce sufficient parasitoids that we can release adults on a weekly basis beginning in July 1999. We have asked for cooperators to assist us in finding potential release sites for the parasitoids. Permission to release Tamarixia radiata was received on July 12, 1999. The first releases will be made in citrus groves near Fort Pierce and Indiantown on July 15, 1999.
We continue to watch and wait for the pink mealybug. As soon as it is confirmed present in Florida, we expect to import and evaluate parasitoids for release in Florida.
Funding: FCPRAC Grant:$17,000 plus + $15,000 (allocated July 98): $32,000
Optimal Timing and Placement of Entomophagous Nematodes for Control of Diaprepes abbreviatus
Project No. 971-27
Investigators: P.A. Stansly
L.W. Duncan
IFAS - Immokalee/
Lake Alfred
Abstract
Formulations of entomomphagous nematodes are the only available option to control larvae of Diaprepes abbreviatus. However, there has been little consistency with results using standard application methods and recommended rates. A uniform application can be made with the herbicide boom, but nematodes cannot easily penetrate beyond the zone wetted by irrigation except with the help of rainfall. Variable output is often seen with micro-irrigation and nematodes cannot be placed outside the wetted zone. We studied application methods (1998) and rates (1999) to better define necessary conditions to obtain satisfactory control of Diaprepes with nematodes on a commercial scale in Flatwoods citrus.
Objectives
(1) Develop and refine techniques for evaluating the impact of nematode
on Diaprepes populations
(2) Assess methods and timing of nematode applications
(3) Determine rate of commercial nematode formulations necessary to
effect satisfactory control
Summary of Accomplishments
Field Experiments 1998. We applied two nematode products in large replicated plots in two flatwoods groves, one on microsprinklers and the other on drip. Treatments included BioVectorä (Steinernema riobrava) applied by single and split applications through irrigation and single boom application as well as Grubstakeä (Heterorhabditis bacteriovora) in a split boom application. Nematode numbers sampled at drip emitters increased with distance from the source, until near the end of the line where only few were discharged. Discharge of nematodes from microjets decreased with increasing distance from the injection point. Apparently, there was insufficient turbulence in the lines to maintain nematodes in suspension. Only a few nematodes were recovered by Bereman extraction, mostly from soil collected close to the drip emitters. Field and lab bioassays showed no differences between treatments and controls, nor did Tedders catches.
Bioassay Negative results in 1998 caused us to re-evaluate basic assumptions. The nematodes clearly worked in the laboratory when confined with their weevil host. Reported experimental results from field or simulated field studies clearly demonstrated activity, but rates per unit surface area were often higher than labeled rates by orders of magnitude. It would appear that only a fraction of the nematodes were actually reaching the target site, so we elected to increase the rate. To better evaluate the effects of rate in the field we developed a bioassay that could provide quantitative estimates of nematode activity in the soil. We were able to develop mortality response curves using medicine cups filled with sterile soil that differentiated between rates of 10, 100, and 1000 and 10,000 nematodes added as a suspension.
Field Experiments, 1999 At the best of our 2 field sites we applied liquid BioVector at 1x, 2.5x and 10x with the herbicide boom (micro-sprinklers running) at recommended rates in early July. Products arrived in good shape and survived the application process. Field soil assayed in medicine cups with Diaprepes showed significantly higher mortality than background (40%) from soil treated with the 2.5x and 10x rates of BioVector at 12 hours and with the highest rate at 5 days. No additional activity was detected at 12 days compared to background. So far we have seen no differences in trap counts (both Tedders and cone) although it is still early. We are planning to make a second application in September, so that final rates will be 2x, 5x and 20x for BioVector and 2x for Grubstake. We hope that this experiment will provide some benchmark rates for nematode effectiveness.
In a separate experiment, we evaluated a micro-sprinkler application in a system that exceeded 95% uniformity. Range of output among lines within zones varied by only 12%. Estimated nematode output was consistent down each line except for the last emitter. These results demonstrated that micro-sprinkler irrigation can provide a satisfactory distribution of nematodes, at least under ideal conditions. Our next objective will be to define the minimum parameters necessary to achieve this goal.
Funding: FCPRAC Grant $17,000
Diaprepes Damage and Interactions with Phytophthora
Project No. 971-45
Investigators: J.H. Graham
C.W. McCoy
IFAS-Lake Alfred
Abstract
Larvae of Diaprepes abbreviatus are causing devastating tree losses in about 30,000 acres of the citrus industry and the weevil's spread is accelerating rapidly. Due to the lack of early detection methods and highly effective control options for the weevil, citrus over much of this acreage is in decline or out of production. Phytophthora species and Diaprepes form a complex that causes severe structural root damage, especially in the presence of a newly discovered root pathogen,P. palmivora. This Phytophthora pathogen is of greater concern than P. nicotianae because it breaks resistance of the rootstock, Swingle citrumelo.
Objectives
1. To survey weevil-infested groves for Phytophthora spp. and damage to large structural roots of trees on susceptible and resistant rootstocks to fungal infection with emphasis on P. palmivora and the associated tree decline in the east coast region of the citrus industry.
2. To quantify the contribution of Phytophthora spp. to decline of young trees on susceptible and resistant rootstocks through selective control of the weevil and the fungus with the biocontrol nematode, Steinernema riobravis, and the fungicide, Ridomil Gold.
3. To evaluated the efficacy ofRidomil Gold for control of structural root infections in groves under IPM management for Diaprepes.
Summary of Accomplishments
In Diaprepes-infested areas on the east coast, Phytopthora palmivora is a major contributing factor in the decline of trees on Swingle and Carrizo. Damaging populations of P. palmivora also occur in association with water-damaged roots, heavier soils, on Swingle and Carrizo rootstock.
Major differences occur in the interaction of Diaprepes with the two major species of Phytophthora and rootstocks. If initial weevil damage on Cleopatra mandarin and trifoliate orange seedlings exceeds a threshold, subsequent damage by P. nicotianae increases on P. nicotianae-susceptible Cleopatra but not on resistant trifoliate orange. Conversely, when weevil-damaged roots of trifoliate orange and Swingle are challenged with P. palmivora, damage is greater on these rootstocks than Cleopatra. This result supports field observations that greater decline after weevil damage occurs on rootstocks susceptible to each Phytophthora species in a given situation. Thus, use of Swingle as a tolerant rootstock will depend on which Phytophthora species is prevalent in weevil-affected groves. Because Swingle is susceptible to P. palmivora, this rootstock may not be acceptable for replanting groves when Diaprepes and this Phytophthora species are present.
In a field trial with young trees in Vero Beach, transplant of Valencia trees on Swingle pre-infested with Diaprepes increases subsequent damage by P. palmivora and P. nicotianae compared to non-infested trees. Damage of fibrous and tap roots by Phytopthora species exceeds that of the weevil. Fungal damage is reduced by Ridomil even when larval damage is pre-established. Root damage of larvae-infested trees is not reduced by a single application of Steinernema riobravis prior to planting.
Funding: FCPRAC Grants: $ 37,250
Classical Biological Control of Diaprepes abbreviatus
Project No. 981-42
Length of Project: 3 years
This report is for year Number 1
Investigators: J.E. Peña,H.Browning,
J.Knapp & C. McCoy - IFAS -Homestead
& Lake Alfred; R. Bullock - IFAS - Ft. Pierce;D.Hall-U.S Sugar Corp-Clewiston; S. Lapointe-USDA - Orlando
P. Stansly-IFAS-Immokalee;R.Adair -
Kerr Center, Vero Beach; J. Etienne
INRA, Guadeloupe and Ru Nguyen - DPI-Gainesville
Abstract
Classical biological control of Diaprepes abbreviatus offers the promise of providing long term, relatively inexpensive control that can be part of sound management of the root weevil. This proposal investigates the success of biological control of Diaprepes abbreviatus in citrus orchards through exploration, collection, identification, introduction, of exotic egg and adult parasitoids of the root weevil from regions where species of Diaprepes are maintained under sub-economic damaging levels. Promising biological control candidates are mass -reared, released in citrus orchards and their establishment evaluated in different citrus producing areas. If successful, biological control will reduce production costs by reducing pesticide applications in citrus orchards.
Objectives
1. Enhance biological control of the borer weevil in south Florida through rearing, release and establishment of the exotic egg parasitoid Ceratogramma etiennei.
2. Explore for, collect, identify and import additional parasitoids of different stages of the pest, i.e., parasitoids of eggs and adults from the Caribbean, Central and Northern South America where populations of Diaprepes spp or related species are kept under non-economic levels.
3. Mass-rear successful candidates and release them in citrus orchards after careful assessment of their potential as biocontrol agents.
Summary of Accomplishments
During 1998-1999 we introduced, reared, and released 180,000 adults of the specific egg parasitoid Ceratogramma etiennei in citrus orchards located in 8 Florida counties. However, with the exception of a single collection of these parasitoids in the area of Clewiston, no other recoveries have been made in the citrus growing areas. The egg parasitoids, Haeckeliana spp., (Hymenoptera: Trichogrammatidae) and Quadrastichus spp., were imported from Colombia and the adult parasitoids Psychophagus n. sp., (Hymenoptera: Pteromalidae) and a Tachnid fly (Oestrophasia nr. signifera) were imported from Mexico and tested against D. abbreviatus. None of the imported parasites accepted D. abbreviatus as a host. Candidate parasitoids, i.e., Aprostocetus vaquitarum were introduced by C. W. McCoy from Dominican Republic and are currently being tested against D. abbreviatus under quarantine conditions. Exploratory trips will be conducted in Haiti, Jamaica and Guadeloupe to collect and introduce into Florida other parasitoids of the root weevil or related species. All introduced parasitoids will be tested to determine their promise as biocontrol agents of D. abbreviatus. Promising candidate parasitoids will be released in citrus orchards after permission to release is obtained from DPI and APHIS-PPQ.
Funding: FCPRAC Grants $34,960
Classical Biological Control of the Brown Citrus Aphid
Project No. 981-50
Length of Project: ca. 4 years
This report is for Year Number 1
Investigators: M.A. Hoy
IFAS - Gainesville
Ru Nguyen
FDACS - Gainesville
Abstract
The brown citrus aphid is an efficient vector of virulent strains of citrus tristeza virus and also serves as a direct pest of young flush in citrus trees. Our goal is to identify host-specific parasitoids of the brown citrus aphid, import them into quarantine, evaluate them, and, if approved by state and federal regulatory agencies, release them into Florida's citrus groves for permanent establishment. Sites to be searched include Australia, Thailand, and Viet Nam. If we can identify and establish effective parasitoids, the potential benefits of this project include reducing the transmission of tristeza virus through reduced aphid populations, reduced production costs, and the maintenance of biological control of other citrus pests by reducing pesticide applications to suppress the aphids. The aphids are a particularly serious pest in nurseries.
Objectives
1. Identify source of appropriate parasitoids.
2. Obtain permits for importation from Australia and Asia (Viet Nam and Thailand).
3. Collect parasitoids from Australia and Asia (Viet Nam and Thailand).
4. Import parasitoids into quaran- tine.
5. Develop rearing methods.
6. Write environmental assessment.
7. Apply for permission to release parasitoids.
8. Mass rear and release parasitoids throughout Florida.
Summary of Accomplishments
This project began officially on July 1, 1998. During the past year we have maintained citrus trees in culture for rearing the aphids and clean aphid colonies. We obtained permits to import parasitoids of the brown citrus aphid and identified personnel who can help collect parasitoids. I travelled to Queensland, Australia, in November 1998 but did not find appropriate natural enemies at that time; collaboration to obtain parasitoids continues with an Australian colleague. We have also identified parasitoids from brown citrus aphid in Viet Nam and Guam and have asked cooperators there to rear them for identification. During June 1999, the first shipment was sent from Guam to the quarantine facility in Gainesville. Unfortunately, all parasitoids were killed in transit, but another shipment is expected during the second week of July 1999.
Funding:FCPRAC Grant $16,000
ENTOMOLOGY
Completed Projects
Attractants and Oviposition Stimulants for Diaprepes abbreviatus:Field Evaluation of Traps
Project No. 942-56
Investigators: H. N. Nigg
IFAS - Lake Alfred
S.E. Simpson
FDACS-Winter Haven
Abstract
Detection of Diaprepes root weevil is an important tool for most Florida citrus growers. Presently, detection methods are limited to the following: Tedders traps, cup traps, emergence traps, and the umbrella technique. This proposal investigates the efficiency of each method to provide a population estimate. This estimate can provide the grower with data that will be used for scheduling treatment for adult weevil control.
Objectives
The objectives of this funding cycle for this project were to:
1. determine the efficiency of the Tedders trap.
2. bioassay attractants in the laboratory.
3. bioassay oviposition stimulants.
Summary of Accomplishments
This has been a highly successful project. The data provided by this project provides a basis for future attractant work.
The efficiency of the Tedders trap and a cup trap was determined in the field. The efficiency of the umbrella technique for collecting adult Diaprepes abbreviatus L. was evaluated in the field. An assessment of the Tedders trap efficiency under controlled conditions was conducted.
The placement of traps in relation to the tree was important for maximum unbaited efficiency. The Tedders trap caught about 1 weevil per 100 in the field when placed midway between the trunk and the dripline. The cup trap had an efficiency of about 1.5 weevils per 100 when placed in the tree. Other placements of the cup and the Tedders trap in the field were less efficient.
The umbrella technique captured 65% of the weevils present and had a detection rate of 75%. This efficiency provided a population estimate upon which to base the efficiency of the Tedders trap.
A dependable and repeatable bioassay was developed for feeding stimulants for D. abbreviatus.
Funding: FCPRAC Grants: $ 12,500
Field Evaluation of Natural Enemies of Brown Citrus Aphid, Toxoptera citricida, in Florida Citrus.
Project No. 971-16
Length of Project: 2 years
This report is for year: No. 2
Investigators: J.P. Michaud,H.W. Browning
IFAS- Lake Alfred
Abstract
Brown citrus aphid (BCA) was discovered in Florida in November of 1995 and, in less than 3 years, has infested virtually all regions of commercial citrus production in the state. The high efficiency with which BCA vectors citrus tristeza virus (CTV) is a primary concern to citrus growers. In particular, the prevalence of strains of CTV causing 'quick decline' on sour orange rootstock has forced growers to abandon this variety for new citrus plantings and is expected to result in the loss of some 20 million producing trees within a 5 year period. Our task over the past 2 years was to assess the potential for biological control of this pest, by means of both native and introduced species, and develop the components of an integrated management strategy.
Objectives (1998 & 1999)
1. Identification of indigennous natural enemies and quantification of their impact on BCA.
2. Evaluation of the introduced parasitoid Lysiphlebia japonica.
3. Detection and characterization of BCA overwintering sites.
4. Laboratory experiments to measure the aggregation tendency of BCA alates.
5. Field and laboratory evaluation of lacewing larvae as a 'biopesticide' against BCA.
6. A study of the effect of aphid load on flowering and fruiting in sweet orange.
Summary of Accomplishments
We studied 16 cohorts of BCA in citrus and followed some 1200 aphid colonies to extinction. On average, less than 5-10% of BCA colonies mature to produce alates which vector CTV. We identified 19 coccinellid species, 6 syrphids species, 3 lacewing species, and miscellaneous other predators of BCA in Florida. The imported parasitoid, Lysiphlebia japonica, was found to be ineffective against BCA in Florida. The primary causes of BCA mortality were coccinellids in spring, syrphids in summer, and a combination of both in the fall. BCA has little difficulty surviving the winter in Florida; small populations persist on root sprouts and any asynchronous citrus flush. Hot summer weather imposes considerable mortality on BCA populations; surviving colonies occur on shaded interior flushes. Alate BCA display a tendency to aggregate on the most suitable citrus terminals, a strategy for improving colony survival. We evaluated green lacewing larvae from a private insectary for possible use as a 'biopesticide' against BCA. Larvae consumed large numbers of BCA in the laboratory and readily accepted this aphid as prey in the presence of alternatives. Although few larvae completed development on BCA, larvae failing to survive fed just as long as those pupating successfully (» 15 days). However, this lacewing species was not effective in two field trials, possibly because it does not venture out on exposed citrus terminals where aphid colonies occur. Excellent natural control of BCA by coccinellids during spring of 1999 precluded a study assessing the impact of infestations on flowering and fruiting.
Funding:FCPRAC Grant $10,000
Assessment of the Potential Impact of Citrus Rust Mite Dispersal on Management Programs and Field Validation of a Trap-Based Monitoring System
Project No. 971-51
Length of Project: 2 years
This Report is for Year Number 2
Investigators: J. C. Bergh
C.W. McCoy
IFAS - Lake Alfred
Abstract
Citrus rust mites disperse on the wind and many mites leaving an infested grove can successfully travel to a downwind grove several hundred feet away. Dispersing mites can be captured in sticky traps, which may have utility as a mite monitoring tool. For this purpose, omnidirectional traps are more efficient than unidirectional traps. Preliminary data suggest that the effect of trap placement within the grove, trap diameter, and trapping interval need to be examined to maximize the operational utility and efficiency of traps for mite monitoring. To understand the impact of dispersal on mite management programs, further field research relating dispersal with mite population growth on trees is required.
Objectives
1. Compare the relationship between mite trap-catch and population density on fruit generated by trap pairs placed in tree rows and row middles.
2. Compare the relationship between mite trap-catch and population density on fruit generated by 7-day versus 14-day trapping intervals.
3. Compare the relationship between mite trap-catch and population density on fruit generated by small versus larger diameter omnidirectional traps.
4. Assess and compare the impact of rust mite dispersal on the growth of mite populations in groves downwind of infested and uninfested groves.
Summary of Accomplishments
The effect of trap placement, diameter and trapping interval on the relationship between mite density and trap-catch was examined at 6 commercial groves in 1998. Omnidirectional traps (1" diameter) in row middles for 7 days yielded stronger data than traps in skips in tree rows, although the range of r2 values among groves was unacceptably large (0.004 - 0.72 skips, 0.02 - 0.88 middles). Larger (1") and smaller (0.5") diameter traps in row middles for 7 days performed equally well, although the range of r2 values among groves was also unacceptably large (0.005 - 0.74 for 0.5", 0.02 - 0.88 for 1"). The strongest relationships were provided by 1" traps in row middles for 14 days, although those were also inconsistent among sites (r2 = 0.01 - 0.98). Data from several years of field validation of these traps leads us to conclude that their utility as a predictive tool for monitoring mite populations is prohibited because of the inherent variability associated with both the dependent (trap-catch) and the independent (population density) variables.
Due to circumstances beyond our control (low populations, pesticide overspray, Hirsutella thompsonii infection) our attempts to assess the impact of dispersal on the rate of population growth at 3 sites were only partially successful. Data collected over 3 weeks at 1 site showed a large movement of mites into the block and onto fruit, although during that short period we could not compare differences in the growth of populations in blocks downwind of infested and uninfested blocks.
Funding:FCPRAC Grants $15,000.00
Monitoring Procedures and Action Thresholds for Thrips Causing Ring Spot Rind Blemish to Red Grapefruit in Florida
Project 981-47
Length of Project - 1 year
Investigators: P. Stansly
C. Childers
IFAS-Immokalee/
Lk. Alfred
Abstract
Rind blemish at the touch points of red grapefruit clusters or between fruit and leaves or twigs has been common in Florida, and has caused packinghouse eliminations due to ring spot. Most ring spot damage on Florida grapefruit has been attributed to orchid thrips, a species of Danothrips and the greenhouse thrips. Insecticidal control of these thrips species is effective, but no sampling method had been developed to evaluate thrips populations and predict damage. This research was an attempt to provide a system for monitoring damaging thrips species, and an action threshold above which thrips should be controlled on red grapefruit to avoid losses from ringspot rind blemish.
Methods and Approach
Plots were located in 2 large blocks of mature red grapefruit in southwest Florida. Each block was divided into 12 plots 9 rows wide by 20 trees long. Four treatments were assigned to these plots in a randomized complete block design with 3 replications. The treatments were threshold levels at which the trees would be sprayed: 10%, 20% 40% fruit clusters infested and a control. Weekly samples were initiated in June and continued through 18 Nov. Each sample consisted of a visual inspection using a 5x headset on 20 fruit clusters. A visual estimation of ringspot injury was also incuded beginning 24 Aug. In addition visual samples, 10 clusters per plot were washed in alcohol and the sample examined under a steroscopic microscope for thrips. A total of 17 alcohol samples were taken weekly or every other week at both sites from 3 June to 19 October.
Results and Discussion
Populations of thrips at CPI were very low throughout the season. No more than 2 were ever found in alcohol samples of 100 clusters. The highest percentage of clusters with damaged fruit ever observed was also 2%.
Target thrips populations at the one grove in alcohol samples were low to moderate, reaching a maximum of about 13 per 100 fruit clusters on 13 Aug. However, no thrips were seen in the visual sample on that date. The maximum number of target thrips observed in visual samples was 8 in 200 clusters on 15 Sep or 4%. However, no spray was triggered because incidence was below the 10% threshold.
Incidence of damaged clusters was 3% on 25 Aug. and reached a maximum of 29 % on 19 Oct. This damage could probably have been avoided if a spray had been triggered by the 13% thrips incidence level seen in the alcohol samples taken on 25 Aug. However, the alcohol sampling and evaluation procedure was considered a research tool and not a practical method for growers. Alcohol samples were not processed immediately because their purpose was as a check for the visual sample. Therefore, no spray was triggered, even though the 10% threshold had been reached on 25 Aug.
The 3% incipient damage level might be a more practical threshold for grower evaluation than 10% thrips incidence. Our plans for the 1999 season are to evaluate the use of damage incidence levels as the criterion for triggering sprays. Treatments could be triggered at the first observed injury, at 3% and by the calendar (post-bloom), with an untreated control. Alcohol samples would again be used to follow thrips populations. We plan to work again in at least locations, possible the same two blocks at Duda, and add a 3rd location if one can be found with higher levels of thrips infestation. Plot size and number of replications will be increased to reduce variation.
Conclusions
Although we were only funded for 1 of the 2 years requested, there was significant progress made on this project:
(3) The alcohol was method of estimating thrips populations for research purposes was validated.
(4) Direct evaluation of thrips populations by the grower was determined to be impractical.
(5) A tentative action threshold of 3% incipient damage was determined. Had the project continued into the second year we would have attempted to validate this action threshold. Nevertheless, should interest in controlling rind blemish problems increase in Florida our results should provide a good starting point for future research.
Funding:FCPRAC Grant $26,000
A Diaprepes Population Estimations System for Citrus Growers
Project No. 981-53
Length of project: 2 years
Investigators: H. N. Nigg
IFAS - Lake Alfred
S.E. Simpson
FDACS-Winter Haven
D.G. Hall- US Sugar- Clewiston
Abstract
Managing a Diaprepes root weevil infestation is expensive and long-term for many Florida citrus growers. A large portion of the operating cost for production is spent on control tactics or strategies. This proposal investigates an accurate and practical method for estimating the population. Management efficiencies will be improved with increased yields of the infested areas.
Objectives
The goal of this proposal is to provide growers with an accurate and practical method for estimating the level of Diaprepes abbreviatus infestation and consequently making an informed decision on control measures. Various sampling and assessment methods will be compared for accuracy and ease of use by a citrus grower. At the end of this two year project we expect to recommend where to look for this weevil, when to look for it, how to look for it and how to use this information to control it.
Diaprepes abbreviatus treatment is an ‘iffy' proposition because it is not known how the sighting of an adult or feeding signs relates to the size of an infestation. On the other hand, a large, visible and feeding population is usually treated. The difficulty is that a large visible population means the grove is infested; that control measures will be more extensive.
A practical method for estimating an adult population would allow treatment options before the population becomes difficult to manage.
Objective
To determine an appropriate sampling method for Diaprepes adults which can be used to obtain a population estimate.
Summary of Accomplishments
This project has been successful in its first year. We have assessed the efficiency of the Tedders trap in a release experiment. Overall about 28% of weevils went to the Tedders traps. If the weevil was between the tree and trap this percentage dropped to 17%, but with the trap between the weevil and the tree the trap percentage was about 40%.
We reanalyzed a 65 week Diaprepes trapping experiment to determine the number of trees to sample to detect and estimate a population of Diaprepes adults. We have set protocols and have selected 2 central Florida, 1 north and 1 south Florida citrus groves for this experiment.
Funding:FCPRAC Grants: $19,0000
Listening to the Larvae: Acoustic Detection of Diaprepes abbreviatus
Project No. 981-57
Length of Project: 3 years
Investigators: R. Mankin,
S. Lapointe - USDA-Gainesville
C. McCoy,H. Nigg - IFAS-Lake Alfred
Abstract
The citrus root weevil, Diaprepes abbreviatus, costs growers >$70 million yearly in fruit and tree loss and control treatments. Most losses are due to hidden damage to tree roots caused by the subterranean larvae. Growers need new tools to assess larval infestation and reduce management costs. Researchers must determine the efficacy of nematodes and other larval management strategies. New acoustic methods have been developed to detect subterranean larvae using accelerometers, tape recorder, and headphones. Our proposal was to investigate the potential of these acoustic methods for development into practical detection and monitoring tools. This technology can contribute to growers' profitability by: 1) Decreasing treatment costs by identifying infested groves or sections of a grove; 2) Providing a tool to determine the efficacy of larval treatments; and 3) Enabling regulators to assess larval populations and reduce dissemination of adults. The objectives for the 3-year project are outlined below.
Objectives
1. Improve field sampling methods.
2. Improve analysis methods for interpreting discriminating insect signals from background noise.
3. Devise a portable and low-cost system.
4. Correlate larval with adult populations.
Summary of Accomplishments
In Year 1, improvements were made in procedures for deploying the acoustic system in citrus groves, and in development of digital signal processing techniques to identify Diaprepes sounds and distinguish them from background noise. We evaluated the effects of different environmental conditions and background noises, and compared listeners' estimates of insect activity with those of the computer. Whenever possible, we collected soil samples or pulled trees to compare the estimates with the actual numbers and types of organisms present. A portable system was developed with a long spike that could be quickly inserted at an angle to pass close to the crown of the root system where the larvae cause the most damage. The results have been presented at an Acoustical Society of America Conference, a Soil Science of America Conference on Agroacoustics, and at Florida Entomological Society meetings. A paper is in review for submission to the Journal of Economic Entomology. On May 20, an acoustic system was demonstrated successfully at a Diaprepes Task Force meeting in an infested grove near Labelle.
We are pleased with the success of the project in meeting Objectives 1-2 during the first year, and have begun a new experiment at the ARS laboratory in Plymouth to monitor the effects of nematode treatments on Diaprepes activity. We will be asking for continued support from FCPRAC that can be leveraged with USDA funds to continue rapid development and application of the acoustic detection system.
Funding:FCPRAC Grants $ 22,620
Biological Control by Egg Parasitoids of Diaprepes abbreviatus in Citrus
Project No. 981-58
Length of Project: 3 years, cancelled by FCPRAC after 1st year
Investigators:D.G. Hall, U.S. Sugar Corp.- Clewiston; Ru Nguyen, FDACS-
Gainesville; P.A. Stansly, IFAS - Immokalee
Abstract
The root weevil Diaprepes is a serious threat to the citrus industry in Florida. Larvae of the weevil can cause substantial damage to roots resulting in decreased production and sometimes plant death. Chemical treatments can help reduce population levels of adults and eggs, but these are costly and can disrupt management programs in place for other pests. Biological control of eggs by parasites would be an attractive, environmentally-sound IPM strategy. Reports from the Caribbean and West Indies indicate that Diaprepes eggs are often attacked by parasites.
Objectives
The objectives of this research project were to evaluate biological control of Diaprepes eggs in Florida citrus and, if possible, to establish or boost biological control of the pest. Biological control could help reduce overall infestation levels of and damage by Diaprepes, which ultimately might reduce the need for other IPM strategies such as chemical control treatments.
Summary of Accomplishments
Eggs of Diaprepes were routinely monitored in Florida citrus groves infested by the Diaprepes abbreviatus during 1998 to determine if egg parasitoid species were present. The research was conducted at nine locations in Florida including the following counties: Hillsborough, Polk, Orange, Glades, Hendry, St Lucie, Indian River and Dade. One location was studied in Puerto Rico. No native parasitoids attacking D. abbreviatus eggs in citrus were discovered in Florida. In contrast, an average of 33.4% (range 12.9 to 68.8%) parasitism of weevil egg masses was observed in citrus sampled in Puerto Rico. Quadrasticus haitiensis and Horismenus spp were recovered from egg masses of D. abbreviatus in Puerto Rico. The Horismenus parasitoids were suspect hyperparasites. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were made during 1998 at each of the Florida research sites. C. etiennei had been recovered only once when this report was written. Apparently due to fund limitations, FCPRAC cancelled this 3-year project after the first year.
Funding:FCPRAC Grants $28,200
Automated Ground Release Equipment For The Dispersal of Biological Control Agents
Project No. 981-60
Investigators: R.E. Burns
D.L. Harris
S.A. Hildebrandt
FDACS-Gainesville
T.C. Holler
USDA-Gainesville
Abstract
The use of biological agents to combat pests in Florida's agricultural industry has become increasingly important. One current method of biological pest control involves releasing sterile Caribbean fruit flies into large wild Caribfly populations. The current method of release for Caribflies and other biocontrol agents is using static release, which appears to be an inefficient and costly method of release.
This proposal involves the purchase, testing, and subsequent incorporation of prototype automated ground release equipment as an alternative to the static release method. This equipment, recently developed by the USDA but only briefly field tested, allowed for the release of larger quantities of biological control agents (insects) in a more efficient manner and across a broader geographical area. A test of the equipment will consist of an experimental design to compare the efficiency of automated vs. static release using sterile Caribflies and the quality of the insects dispersed using these methods.
Objectives
1. Compare the automated release equipment with current static release methods.
2. Evaluate the automated release equipment for various types of biocontrol agents (sterile flies, parasites, etc.)
3. Analyze release process for quality of release agents, efficiency, and economic savings.
4. Develop recommendations for release mechanisms based on process analysis.
Summary of Accomplishments
Initiation of the project was delayed from April 1, 1998 to June 1, 1999 due to the unavailability of the automated release equipment from the USDA cooperator. This problem was due in part to various emergency fruit fly programs which occurred in 1998 in Florida, California and Latin America.
Recent negotiations with the cooperator has made that equipment available and the formal initiation of the project occurred on June 1, 1999. The same methods and approach as originally outlined will be used to complete the project. A revised time will be: Initiation of test program - June 1999; Completion of test program - December 31, 1999.
Funding:FCPRAC Grants $ 25,000
PLANT IMPROVEMENT
Continuing Projects
Development and Evaluation of Improved Citrus Rootstocks
Project No. 928-27
Length of Project: 20 years
Investigators: J.W. Grosser,F.G. Gmitter, Jr.,W.S. Castle
IFAS - UF - CREC
Abstract
The goal of this project is to develop the improved rootstocks that the Florida industry will rely on to remain competitive and profitable in the future, and to provide growers with information necessary to make the best rootstock choice for any situation. When new rootstock germplasm is developed and reaches an advanced stage of evaluation, the plant material goes into commercial trial, and appropriate data entered into formalized decision-making models. New improved rootstocks will help Florida growers to compete internationally. Tree loss and associated production losses, and tree replacement costs will be minimized. Citriculture will have a
reduced impact on the environment through the biological control of diseases, thereby reducing chemical applications. New, widely adapted rootstocks will allow citriculture to expand into marginal areas. Overall, growers can expect savings in production costs, more continuous and higher productivity, and increased tree longevity.
Objectives
1. Develop improved rootstocks that when budded with a scion, produce long-lived, compatible trees that yield large quantities of high quality fruit and juice, and tolerate the diseases, pests and environmental stresses that occur in Florida.
2. Improve the characteristics of existing selected commercial rootstocks.
3. Develop and employ appropriate rootstock evaluation procedures and up-to-date techniques for comparative financial analyses evaluation data and expert system models in order to give growers sophisticated approaches to rootstock selection.
Summary of Accomplishments
Sexual Hybridization Program: Seeds were harvested and planted from crosses made using Flying Dragon as female (to capture the possible tree-size control from FD cytoplasm) with pollen from Duncan, Ridge Pineapple and sour orange, to increase the numbers within these families. Pimpled mandarin (an introduction from China with tolerance of cold, drought and salinity) was hybridized with Palestine sweet lime x C.ichangensis hybrids that combine vigor with cold hardiness. In 1999, crosses with FD as seed parent were repeated with the 3 pollen parents above, plus Kinkoji and a CTV-immune pummelo x trifoliate hybrid. Kinkoji, Cleo, and the Pimpled mandarin were also hybridized with the P x TO hybrid, FD, salinity- and high pH tolerant C. limonia selections, and Cleo x FD, and Cleo x Swingle hybrids, selected for fertility. A total of 15 families were attempted following over 1200 controlled pollinations.
Somatic Hybridization Program: Planted phase F of the SandRidge rootstock trial (37 trees of Valencia somaclone N12-11 on 3 somatic hybrids, x639, and Carrizo). Completed propagation of a Flame/Rio Red grapefruit rootstock trial for Fort Pierce (20 trees/rootstock, 30 rootstocks including 20 somatic hybrids). Continued propagation and planting of new material into blight hotspots (with Orie Lee). Collected seed (for the first time) and propagated 200 liners of Nova + HBP and sour orange + Carrizo somatic hybrids (both promising hybrids) for use as replacements in the Sandridge trial. Produced 6 new somatic hybrids, including Changsha mandarin + trifoliate orange, Milam + HBPummelo, Meiwa + HBPummelo, and Meiwa + rough lemon (emphasis on adaptation to high pH calcareous soils, and tolerance to the Diaprepes/Phytophthora complex).
Continuing Field Trials: 1) A Hamlin continuing rootstock trial was terminated after collecting 10 years of yield and juice quality data. Leading rootstocks for PS production were Benton, Carrizo, and Troyer citranges (10-20% more productive than Swingle). Trees on SFS, Cleo,Kinkoji, and others performed like Swingle. Promising rootstocks include x639 and C-35. 2) In a 6-year old Hamlin trial, trees on C-32 and Morton citranges have been outstanding for yield. 3)To understand the soil-rootstock interaction, Valencia trees on 7 rootstocks were planted in 5 soil types in the Ft. Pierce area. 4) Yield and fruit quality data were collected (for the first time) from the 6-year old Rohde Red Valencia/somatic hybrid rootstock trial at US Sugar (Clewiston). Promising size control rootstocks include the sour orange + Palestine
sweet lime and Cleo + Argentine trifoliate orange somatic hybrids. 5) Yield and fruit quality data from a Valencia rootstock trial in Martin Co.(Becker Co.) revealed good performance of a CREC-AP hybrid [(pummelo x sour orange} x Orlando], with uniform high yielding, vigorous trees and no decline.
Funding: FCPRAC Grant: $80,000
Utilization of Gene-Mapping and Marker-Assisted Selection for Citrus Variety Improvement
Project No. 942-27
Length of Project: 3 years
Investigators: F.G.Gmitter,Jr.
IFAS - Lake Alfred
G.A. Moore
IFAS-Gainesville
Summary of Accomplishments
1. Genetic markers developed previously for CTV-immunity and citrus nematode resistance have been used to pre-select resistant hybrids from crosses made for rootstock improvement.
2. RAPD markers associated with resistance to Alternaria and Phytophthora have been mapped by MAPMAKER and JOINMAP software packages. Three linkage groups for Alternaria resistance were identified, though the resistance gene mapped only to one of these, along with two RAPD markers. The RAPD markers can be used to discard susceptible hybrids.
3. The results of greenhouse and growth chamber tests for resistance to P. nicotianae and P. palmivora were inconsistent, so marker mapping efforts were abandoned. However, several linkage groups were identified in association with tolerance to Phytophthora nicotianae, as assayed by stem lesion growth in vitro. QTL analysis did not reveal any significant genomic regions that could be used for selection in rootstock breeding. The difficulties encountered in this effort pointed out the inadequacies of Phytophthora screening techniques and the critical need to develop accurate marker-based selection methods.
4. Comparative screening for tolerance of the two Phytophthora species demonstrated clearly that different sources of tolerance must be used in breeding to develop rootstock with tolerance of both.
5. New, highly specific SCAR and RGC markers in tight linkage with nematode resistance were developed to improve accuracy of marker-assisted selection.
6. Markers in genomic regions controlling cold-tolerance have been identified in 2 populations.
7. Mapping of bioflavonoid genes is in progress, and carotenoid genes were recently cloned for future mapping.
Funding:FCPRAC Grants: $ 49,000
Funds allocated to Dr. Gmitter from FCPRAC -- granted project for rootstock cultivar improvement, 928-27; this project is indirectly related to 942-27.
Field Evaluation of Promising USDA Rootstock Selections
Project No. 981-30
Investigators: K.D. Bowman
H.K. Wutscher
USDA - Orlando
Length of Project - 3 Years
This Report is for Year 1
Abstract
Use of an appropriate rootstock is the most effective way to reduce future tree losses and increase profits in new plantings and replant situations. Several new USDA hybrid rootstocks have already been shown to be resistant to Phytophthora and blight, tolerant of tristeza and cold, and produce trees that yield larger quantities of high quality fruit than standard commercial rootstocks at some sites. The proposed research will help identify which superior new rootstocks should be released to the industry from among the selected advanced hybrids. Trials with these new hybrid rootstocks have been established at several locations around Florida. Support for this project will be primarily used to collect complete performance information from these trials, including yield, fruit quality, tree size and health, disease and pest damage. The project will also support establishing new rootstock trials and demonstration blocks at additional sites.
Objectives
Collect field performance information on advanced USDA rootstock selections in trials and demonstration blocks.
Coordinate propagation of advanced USDA rootstock selections and establishment of trees for new field trials and demonstration blocks at additional sites.
Prepare summaries of field performance information on advanced USDA rootstock selections.
Summary of Accomplishments
Performance information on new rootstocks was collected from several producing rootstock trials and new trials were established in several areas. Results from trials in Lake, Polk, Osceola, and Indian River Counties indicate that new USDA rootstocks under evaluation may be superior to existing rootstocks for some common production conditions. More widespread testing of new rootstocks was initiated by placing multiple test trees as replants in cooperator groves and tracking these with GPS/GIS technology. Rootstocks identified as US-852 (Changsha x English Large Flowered trifoliate orange), HRS-812 (Sunki x Benecke trifoliate orange), and HRS-942 (Sunki x Flying Dragon trifoliate orange) were identified as especially promising for densities of about 150 trees per acre and are included in new rootstock trials being propagated now for planting this year and next. Other new rootstocks, such as HRS-897 (Cleopatra x Flying Dragon trifoliate orange) and HRS-896 (Cleopatra x Rubidoux trifoliate orange), that produce small trees ideal for higher density plantings are also being included in new trials at several locations. Detailed comparisons of field performance for many new rootstocks were reported in 2 publications in print and at several meetings attended by growers.
Funding:FCPRAC Grants $ 30,000.
PLANT IMPROVEMENT
Completed Projects
Identification and Performance Evaluation of Advanced Scion Selections
Project Number 981-36
Length of Project: 1 Year
Investigators: F.G Gmitter Jr.
J.W. Grosser
W.S. Castle
IFAS-Lake Alfred
Abstract
Thousands of unique plants have been produced by the CREC variety improvement team, to develop new scion varieties for Florida growers.Detailed evaluations of their performance and characteristics have been limited by scarce financial
and personnel resources. Preliminary selections should be made and entered into advanced trials, so selections that are consistently superior can be identified and made available to growers. Some advanced trials already in place should be evaluated more rigorously. The intent of this project is to focus attention on evaluations of scion materials developed at the CREC previously.
Objectives
a. Preliminary screening and primary selection from uncharacterized
families of sweet orange, grapefruit, and mandarin hybrids. More than
13,000 individual trees are being grown, many of which are bearing fruit now.
b. More detailed evaluations of tree and fruit characteristics of
individuals already selected in primary screening, including 125low-seeded Murcott selections and at least 65 Valencia sweet orange
clones with mid-season maturity.
c. Field performance data collection from advanced selections in
replicated trials, including two early and one mid-season mandarin
hybrids, and several early-season, highly pigmented sweet oranges.
Summary of Accomplishments
a. Screened more than 2000 orange, 625 grapefruit, and 100 mandarin
trees for fruit quality traits.
b. Conducted pilot plant tests of over 130 orange selections for
solids/acid ratio, juice %, pounds solids/box, and juice color.
c. Screened over 200 irradiated mandarin budlines for reduced seed
number.
d. Evaluated over 200 second generation trees propagated from low-seeded Murcott mutants produced by irradiation.
e. Collected data on 3 CREC advanced mandarin hybrid selections from a replicated trial on 8 rootstocks.
f. Completed data collection on orange seedling introduction from the Lee Grove, published relevant information in The Citrus Industry, and made public release of the material.
g. Identified over 60 new orange selections maturing across the entire season, with improved processing or fresh fruit qualities and productivity; several improved grapefruit selections; and consistently low-seeded Murcott budline clones. All of these will go to advanced field trials.
h. Through the work listed above, the CREC scion breeding program has made excellent progress toward our goal of developing and releasing new scion cultivars of value to the Florida citrus industry. The seedling introductions that were evaluated and released this year have can have very great impact on the processing and fresh market orange industries, by virtue of their early maturity and high juice and flesh color scores. We have also identified several mid-season oranges for advanced trials that, likewise, are characterized by their excellent color, quality, and what appears to be good productivity. We have found consistently low-seeded Murcott budline clones, which can be beneficial to the specialty fresh fruit industry in domestic and foreign markets.
Funding:
FCPRAC Grants: $ 33,000
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