Progress 10/01/98 to 09/30/04
Outputs
Plant growth regulators (PGRS) were used successfully to increase juice content of processing oranges and yields of some tangerine hybrids. Trees were sprayed with gibberellic acid (GA)in the fall and juice content was increased by 4-10% at harvest the following winter in most cases. GA was also used to increase fruit set and yields of some tangerine hybrids especially Ambersweet. GA also has promise for increasing juice content of processing oranges following a freeze, allowing growers and processors more flexibility in harvesting. Ecolyst,a tertiary amine growth regulator, was applied to orange trees at various times during bloom and increased juice soluble solids by 0-0.38 units. Results only occurred in 5 of 13 trials, however.
Impacts
Based on this research, thousands of acres of Florida oranges have been sprayed with GA for increasing juice weight,and profitability for growers and processors. GA has also significantly improved yields of some Ambersweet groves.
Publications
- Davies, F.S., E. Stover, G.R. Zalman, and S. Ciliento. 2004. Ecolyst application timing and juice corrected soluble solids of processing oranges and grapefruit in Florida. HortTechnology 14:37-42.
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Progress 10/01/02 to 10/01/03
Outputs
Gibberellic acid (GA) increases juice Brix when applied to processing oranges in Florida. There is also some indication that it may affect citrus cold hardiness. We applied GA to Hamlin and Valencia oranges in the fall and monitored juice content changes following a freeze where fruit temperatures reached -3 C for more than 4 hours. GA-treated fruit had higher juice content than non-treated fruit for both cultivars and more importantly juice levels remained higher for 8 weeks following the freeze. The rate of change in juice content over time, however, was similar for both treatments. Maintenance of high juice levels after a freeze is of potential importance to growers and processors because the value of citrus fruit in Florida is based on juice content and Brix. There was no effect of GA on cold hardiness of the tree or fruit under north Florida conditions.
Impacts
Based on this research, thousands of acres of Florida oranges are sprayed with GA for increased juice weight, increasing profitability for growers and processors.
Publications
- Davies, F.S., E. Stover, G.R. Zalman, and S. Ciliento. 2003. Ecolyst application timing and juice corrected Brix of processing oranges and grapefruit in Florida. HortTechnology (in press).
- Davies, F.S. and G. R. Zalman. 2003. Fruit quality sampling of Valencia orange trees. Proc. Fla. State Hort. Soc. (in press)
- Barry, G.H., W.S. Castle, F.S. Davies, and R.C. Littell. 2003. Variability in juice quality of Valencia sweet orange and sample size estimation for juice quality experiments. J. Amer. Soc. Hort. Sci. 128: 803-808.
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Progress 10/01/01 to 10/01/02
Outputs
NAA thinning was compared on `Murcott' trees of three different ages, with applications made in the spring of 2001 at 250 and 350 ppm. At harvest in 2002, NAA increased fruit size in all experiments with little difference between the two rates. Small plot data showed that NAA increased mean fruit weight by 25-34%, decreased fruit per tree by 24-38%, and decreased fruit yield per tree by 4-24%. Packinghouse data were consistent with small plot results: NAA increased production of 64-100 count fruit by 59-100%, even though no fruit were eliminated because of small size in non-thinned controls. In two of the packinghouse assessments, NAA treatments increased packout by 10% of total harvested crop through improved fruit appearance. Crop value was significantly enhanced in only one of three trials that permitted statistical analysis. However, improved return cropping was apparent in all NAA-treated rows the following spring. Previously, we observed that gibberellic acid
(GA) applied at fruit color break increases juice weight of processing oranges, but the mechanism for the increase was unknown. Two hypotheses suggested that GA either increased peel firmness and juice extraction efficiency or that GA reduced peel volume and increased juice content. A series of fruit rheological tests were run and found that GA increased peel shear and tensile strength, but these increases were poorly correlated with juice yield. Alternatively, we found that GA reduced fruit peel volume by decreasing peel thickness and thus increased juice content. GA3 also caused an increase in peel hexoses that may be associated with peel color. MBTA, a PGR reported to increase fruit Brix, was applied at several bloom stages and concentrations to `Hamlin' and Valencia oranges with applications in 2001 and 2002. Modest and variable increases in juice Brix have been observed from some treatments. In the 2001-02 season, MBTA again significantly increased corrected Brix on average by
0.28% for `Hamlin' oranges at the 2 locations, but had no effect on corrected Brix of `Valencia' oranges. There were no cumulative effects of MBTA on fruit quality, yields, tree vigor, or flowering.
Impacts
Based on this research, thousands of acres of Florida oranges are sprayed with GA for increased juice weight, increasing profitability for growers and processors. NAA fruit thinning / size enhancement has greatly increased in Florida citrus and many growers are testing benefits of fall / winter GA to enhance cropping. MBTA has great potential for the processing orange industry in Florida, if parameters can be identified which consistently enhance fruit Brix.
Publications
- Fidelibus, M.W., F.S. Davies, and C.A. Campbell. 2002. Gibberellic acid application timing affects fruit quality of processing oranges. HortScience 37: 352-357.
- Fidelibus, M.W., A.A. Teixerria, and F.S. Davies. 2002. Mechanical properties of orange peel and fruit treated preharvest with gibberellic acid. Trans ASAE 45: 1057-1062.
- Stover, E., S. Ciliento, M. Ritenour, and C. Counter. 2002. NAA thinning of `Murcott': comparison of small plot and commercial harvest data. Proc. Fla. State Hort. Soc. (in press).
- Stover, E.W. Davies, F.S., Ismail, M.A., and T.A. Wheaton. 2002. 2002 Florida citrus pest management guide: plant growth regulators. IFAS Fact Sheet HS-108.
- Stover, E.W., Lin, Y.J., Rosskopf, E., and R. Sonoda. 2002. Assessing potential of Colletotrichum acutatum wild-type and auxotrophic mutants as biological fruit thinning agents in citrus. J. Amer. Pomological Soc. 56:230-234.
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Progress 10/01/00 to 10/01/01
Outputs
Further studies were conducted on the effects of fall and winter GA3 application on flowering and cropping of citrus. For 1999-2000 applications, navel and `Ambersweet' displayed substantial increases in cropping from some GA treatments, with significant differences between different timings. Overall 15 grams per acre of GA3 produced results similar to 20 grams but 10 grams was sometimes less effective. Flowering was significantly affected in `Minneola' and 'Valencia' but there was no effect on yield, even though total flowering was reduced by 40-90%. Fruit size was significantly enhanced in `Valencia' orange and `Ruby' grapefruit when time of flowering was advanced substantially, even though yield was unaffected. In `Late Navel' GA treatments affected time of bloom but total flowering and cropping were not influenced. Studies continue with no harvests yet on 2000-2001 treatments. NAA thinning trials continue in `Murcott', `Sunburst', and `Flame' with a focus on
assessing cumulative response to different thinning programs. MBTA, a PGR reported to increase fruit Brix, was applied at several bloom stages and concentrations to grapefruit in the spring of 2000, with no substantial increase in juice Brix. A wide range of MBTA rates and timings have been assessed on `Hamlin' and Valencia oranges with applications in 2000 and 2001. Modest and variable increases in juice Brix have been observed from some treatments. GA was applied to juice oranges at various times around color break to determine the optimum time of application to increase juice weight. Application at or near color break improved juice weight during processing in some cases, but not others. There was also some indication that GA application reduced juice Brix in some instances. This potential problem is being studied further.
Impacts
Based on the results and recommendations from this research, many thousands of acres of Florida oranges have been sprayed with GA for increased juice weight, increasing profitability for growers and processors. Use of NAA for fruit thinning / size enhancement has greatly increased in Florida citrus and many growers are testing benefits of fall / winter GA to enhance cropping. Substantial increase in `Ambersweet' cropping have been widely reported following winter GA treatments to reduce excessive flowering.
Publications
- Davies, F.S., C.A. Campbell and M.W. Fidelibus. 2001.Gibberellic tank mix and adjuvant effects on peel quality and juice yields of Hamlin oranges. HortTechnology 11:171-174.
- Dou, H., P.D. Petracek, E. Stover, A. K. Alva, D. Calvert, and M.A. Ismail. 2001. Preharvest factors influencing postharvest peel pitting of citrus fruits. Proc. of the Intl. Soc. of Citricult. (in press).
- Fidelibus,M.W. and F. S. Davies. 2001. Gibberellic acid wash-off studies on Hamlin orange. Proc. Fla State Hort. Soc. (in press).
- Fidelibus, M.W. and F. S. Davies. 2001. Gibberellic acid application timing effects on Brix and peel color of processing oranges. Proc. Intl. Soc. Citricult. (in press).
- Stover, E.W. Davies, F.S., Ismail, M.A., Wheaton, T.A. 2001. 2001 Florida Citrus pest management Guide: Plant Growth Regulators. IFAS Fact Sheet HS-108.
- Stover, E.W., S.M. Ciliento, B.J. Boman, and M.S. Burton. 2001. Summary of twenty experiments on NAA thinning of Florida citrus. HortScience 36:522.
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Progress 01/01/00 to 12/31/00
Outputs
The effect of GA application during floral initiation was tested on an array of heavy-blooming but light-cropping citrus cultivars. GA was applied via airblast sprayer near Ft. Pierce, Fla. at 3-5 spray timings during the fall and winter to navel, `Late Navel', Valencia, `Ambersweet', and `Minneola' in 1999-2000. All GA sprays included 0.05% Silwet L-77 and most applications were made at 32 ppm, with lower rates compared at some timings. Trees treated in late November to early December had delayed bloom and some cultivars produced an early vegetative flush that preceded bloom. Late January and early February GA applications typically accelerated bloom compared to controls. Some GA treatments shortened bloom duration 1-2 weeks compared to controls and total flowering was almost always reduced. In several cultivars, trees treated with GA late had little overlap in bloom timing with trees receiving the early GA treatments. Cropping was increased substantially in some
cultivars following fall or winter GA treatments. Hydrogen cyanamide was applied to a range of citrus cultivars to assess potential for influencing bloom. Five citrus species in pots were assessed and varied widely in their phytotoxic response to this compound. Mature navel and Valencia were treated with hydrogen cyanamide at rates resulting in only slight foliar damage and no effects on bloom were observed. In 1999, application of NAA plus surfactant to `Murcott' at two of two sites and `Sunburst' at one of two sites resulted in cropload reduction, increased mean fruit size, and an increase in boxes of large fruit size. NAA was applied to grapefruit at 3 sites in 1999, but harvest in 1999-2000 indicated significant cropload reduction at 2 sites, but size was increased at only one, and fruit size was significantly increased by NAA at one site even though no thinning was observed. Numerous NAA experiments were conducted again in 2000 but have not been harvested. MBTA, a PGR reported to
increase fruit Brix, was applied at several bloom stages and concentrations to orange and grapefruit in the spring of 1999 and 2000. Fruit samples were analyzed at various dates within the commercial harvest window, but increases in Brix thus far have been sporadic. GA was applied to juice oranges at various times around color break to determine the optimum time of application to increase juice weight. Application at or near color break improved juice weight during processing in some cases, but not others. There was also some indication that GA application reduced juice Brix in some instances. This potential problem is being studied further. Several strategies were compared for controlling trunk sprouts on young citrus trees. Latex / NAA spray was less effective than Al foil wraps and resulted in significantly lower increases in trunk circumference.
Impacts
Based on the results and recommendations from this research, many thousands of acres of Florida oranges have been sprayed with GA for increased juice weight, increasing profitability for growers and processors. Advances have been made in effective utilization of MBTA and better recommendations for enhancing fruit Brix will be available for the 2001 growing season.
Publications
- Stover, E.W., Wirth, F., Robinson, T.L. 2000. A method for assessing the relationship between cropload and crop value following fruit thinning. HortScience (in press)
- Stover, E.W. 2000. Relationship of intensity of flowering and cropping in fruit species. HortTechnology 10:729-732.
- Stover, E.W., Ciliento, S.M., Yang, X. 2000. GA3 application timing in fall and winter influences bloom period and intensity and final crop at harvest in Florida `Navel' orange. HortScience 35:496.
- Stover, E. and G. Albrigo. 2000. Enhancing cropping of low-yielding, heavily flowering citrus by reducing floral initiation. Extension Circular
- Stover, E. and G. Albrigo. 2000. Chemical thinning of citrus with NAA for bigger fruit, less branch breakage, and more regular cropping. Extension Circular
- Stover, E., and F. Davies. 2000. Gibberellic acid to enhance juice yield and late-season quality of processing oranges. Extension Circular
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Progress 10/01/98 to 09/30/99
Outputs
The effect of GA application during floral initiation was again tested on several heavy-blooming but light-cropping citrus varieties. GA applied to `Ambersweet' in early January decreased and delayed flowering but had little effect on yield, while application in late January resulted in earlier and decreased bloom but increased cropping eleven fold. Harvest data haven't been collected on `Navel' but flowering was reduced and incidence of leafy inflorescences increased by GA applied from November through January. Time of GA application in `Navel' greatly affected time and duration of bloom, shifting peak bloom by more than three weeks. Late GA applications resulted in early bloom and earlier fruit sizing than non-treated controls. NAA thinning trials in 1998 resulted in increased fruit size at all three `Sunburst' sites but increased crop value at only two sites since the third had good fruit size in non-thinned trees. `Murcott' thinned significantly at 1 of 2 sites
but had increased fruit size at both sites. In 1999, application of NAA plus surfactant to `Sunburst' at two sites and `Murcott' at two sites resulted in visible reduction in cropload and increase in fruit size. NAA also visibly thinned grapefruit at 1 of 3 sites, and fruit size was significantly increased by NAA at one site even though no thinning was observed. Different surfactants and gallon per acre rates resulted in differences in degree of thinning observed. Harvest data will be collected at all sites. Use of GA with Silwet significantly reduced postharvest pitting in `Fallglo' and `Marsh' in 1998-99 but also delayed color development. Combined with risk of GA burn in `Marsh', such treatments appear risky for control of postharvest pitting.
Impacts
(N/A)
Publications
- No publications reported this period
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