Pik-Off (PO), a Ciba-Geigy Corp. product, has been field evaluated under an Environmental Protection Agency (EPA) experimental permit. Although PO does not usually produce as good abscission as some other chemicals, it appears satisfactory for many uses. From a cost and residue standpoint, PO appears to be in an advantageous position, and it is compatible with the ‘Valencia’ cultivar (Citrus sinensis (L.) Osbeck). PO should not be used with surfactants. Its effect is decreased by rain (within 24 hours of application) and low temperatures. PO is restricted by label as to total quantity which can be applied per ha. However, results of a series of volume versus concentration field tests showed that increased amounts of material per ha substantially improved abscission performance, particularly on larger trees.
Various weak acids produce citrus fruit abscission in Florida. Erythorbic (ascorbic) acid (1-2%) or hexamic acid (1-2%), alone or combined with citric acid (total concn 1-2%), produced acceptable abscission but only of early and midseason oranges for cannery use. Phosphoric acid (1/2%) and ferric chloride (0.5-2.5%) produced erratic loosening, phytotoxicity, severe peel injury, and sometimes damaged spray equipment. The type of peel injury resulting from weak acid sprays may cause extensive rotting (40% or more) if extended periods of wet weather occur prior to picking. As weather forecasting is not sufficiently accurate to predict conditions more than 48 hr in advance, and fruit abscission normally occurs from 3-7 days following spraying, the periodic economic losses that could be expected under these conditions preclude their use in Florida.
Sprays of 3-[2-(3,5-dimethyl-2-oxocyclohexyl)-2hydroxyethyl]-glutarimide (cycloheximide) for abscission of early and midseason oranges loosen fruit, but utilizing this response with a shaker + pickup machine harvest system generally show economic gain only on very large trees. Abscission chemicals (abscisors) lend to overloosen the oranges that are easiest to remove, yet fail to loosen adequately those that are normally most difficult to remove. In Florida, current economic conditions do not justify fruit removal much less than 100%. Fruit drops of up to 80% will probably result if abscisors are used to reduce pull forces of nearly all fruits on a given tree to 2.2 kg, the theoretical level desired for mechanical harvesting.
Mechanical harvesting has, of course, long been standard for many annual crops, the “combine harvester” for wheat being an early, and successful, example. In some instances (e.g., tomato, plant breeders have “tailor made” cultivars to adapt them to mechanical harvesting. Typically, such annuals are destroyed in harvesting. The plant must be preserved with perennial crops, although sometimes considerable injury to the plant can be acceptable when (as for grapes or raspberries) the plant is severely pruned annually. Substantial damage to the plant (tree) is not acceptable, in mechanical harvesting of tree crops, but leaf damage is of minor consequence for deciduous tree crops, and the fruit is biologically destined to abscise; if it is not harvested. Damage to the product is not a problem, it will soon fall naturally for some deciduous tree crops (particularly nuts of various kinds). In contrast, mechanical harvesting of citrus fruits involves quite extraordinary problems. The tree is evergreen and substantial leaf damage is not acceptable. The fruit has no clearly defined abscission period. The same grapefruit that might be picked in October can hang on the tree until May. Citrus fruits are extremely subject to decay. ‘Valencia’ (an important cannery orange cultivar) takes 12 to 18 months from bloom to acceptable maturity to complicate matters further. Thus, there are 2 crops on the tree at harvest time; mature fruit that are to be harvested and immature fruit that must not be damaged or removed. It is apparent after 20 years and millions of dollars spent in Florida that the problem (particularly for ‘Valencia’) is as much biological as it is mechanical. The fruit, but not the leaves, must be made to abscise and, for ‘Valencia’, the tree must retain the immature crop while releasing the mature fruit.
Four abscission chemical treatments (Acti-Aid, 20 ppm cycloheximide) (Release, 125 ppm 5-chloro-3-methyl-4-nitro-1H-pyrazole) (Acti-Aid, 5 ppm + Sweep, 250 ppm chlorothalonil + Release, 125 ppm) and (Pik-Off, 300 ppm glyoxal dioxime) were applied to the same orange trees (Citrus sinensis (L.) Osbeck, cv. Hamlin and Pineapple) for 3 consecutive years to aid harvest with a shaker-catchframe system. The treatments had no significant effect on subsequent fruit yield for years not influenced by freezing temperatures.
Two and 3-way combinations of 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), cycloheximide (Acti-Aid), and chlorothalonil (Sweep) were extensively evaluated for fruit abscission and ethylene production responses on ‘Hamlin’ and ‘Valencia’ oranges (Citrus sinensis (L.) Osbeck). The combinations interact synergistically resulting in far greater fruit loosening than would be expected from additive effects of the individual chemicals. The 3-way combinations of Release plus Acti-Aid plus Sweep consistently gave better fruit abscission than the 2-way combinations of Release plus Acti-Aid and required 25% to 50% less abscission chemical compared to individual abscission chemical usage. Increased fruit abscission activity of the chemical combinations resulted from greater peak fruit ethylene production and higher sustained ethylene levels during the treatment period. Distinct fruit loosening and retightening phases were characterized and shown to be correlated with internal fruit ethylene levels.
The demand for hot sauce products continues to expand in the U.S. In the case of jalapeno pepper sauce, there are many cultivars available for sauce production but those best suited for processing have not been adequately determined. Six cultivars (four replications) of jalapeno peppers (`Coyame', `Grande', `Jalapeno-M', `Mitla', `Tula' and `Veracruz') were evaluated for mash fermentation. The attributes studied during mash aging were color spectra, capsaicin content and fermentable sugars. Fructose and glucose were the predominant sugars in jalapeno peppers and these sugars were utilized gradually with time indicating slow fermentation by microorganisms in the 15% salt mash. Capsaicin and dihydrocapsaicin were the predominant capsaicinoids in the jalapeno peppers with `Tula' containing the greatest concentration and `Veracruz' the least. All mashes displayed an apparent and unexpected rise in measurable capsaicinoids up to 6 months with a decline at 12 months. Color changes in the pepper mash were rapid initially but slowed after the first month of fermentation. Percent reflectance in fresh ground peppers was strongest in the range of 550–560 nm but, after salting, reflectance shifted to 580–590 nm and remained throughout the fermentation. Based on the characteristics tested, any of these cultivars would make a suitable mash for sauce. The heat content of the final product could be controlled by cultivar selection or through blending.
Mature Florida ‘Valencia’ oranges [Citrus sinensis (L.) Osbeck] go through a period of reduced response to abscission chemicals. This nonresponsive period is characterized by both a reduction in the amount of ethylene induced by abscission chemicals and by decreased sensitivity of the abscission process to exogenous ethylene. During the nonresponsive period, application of the abscission chemical 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release) induced less ethylene formation and less reduction in fruit removal force than at times either prior to, or following, the nonresponsive period. Experiments with radioactive Release showed that uptake was not a factor in the reduced effectiveness of this material during the nonresponsive period. Abscission of explants induced by exogenous ethylene was slower during the nonresponsive period. Mature ‘Valencias’ also go through a period of regreening. Regreening and the nonresponsive period may begin at about the same time, but regreening continues after the nonresponsive period is over. In addition, color changes induced by exogenous ethylene remain similar throughout the regreening and nonresponsive periods, but abscission of explants induced by exogenous ethylene is reduced only during the nonresponsive period. These differences in time-course and ethylene sensitivity between regreening and the nonresponsive period allow differentiation of these two processes.
The interaction between Cytospora leucostoma (causal agent of peach canker) and host-phenolic compounds in dormant peach trees [Prunus persica (L.) Batsch] was examined. Initially, inoculated samples had significantly higher phenolic levels than uninoculated samples. The levels in inoculated samples decreased dramatically in tissues closest to the point of inoculation, however, while the phenolic levels in uninoculated samples remained relatively stable through time. The data suggested that C. leucostoma degraded host-phenolic compounds. Maximum phenolic enrichment was observed in the branch collar region of the main stem of inoculated samples. It was concluded that the presence of C. leucostoma in host tissue played a significant role, over and above the wounding response, in establishing levels of host-phenolic compounds. Levels of phenolics in host tissue seemed to increase in advance of the fungus and this increase may function as a mechanism that slows the pathogen's advance.