Managing Fruit Maturity and Abscission
Controlling when fruits mature allows more efficient use of labor and other resources, and prolongs the harvest season. For example, PGR applications could advance fruit maturity in one portion of a block, and delay maturity and improve storability in another.
Hastening Fruit Maturity
Ethephon applications will advance apple maturity by 3 to 5 days under favorable weather conditions. This product will also shorten the storage life of treated fruit, so avoid using it on any apples intended for long-term storage.
Ethephon also improves the color of red-skinned apples. Fruit require cool nighttime temperatures and direct exposure to light for color development, even when ethephon has been applied. Proper training and pruning is critical to allow good light distribution within the canopy. Cultivars and strains that color poorly may not respond adequately to ethephon application. Do not use ethephon on yellow or green-skinned cultivars to advance fruit maturity. See the table below for rates and other information.
Ethephon can also speed the process of fruit abscission (fruit drop), and has been used to synchronize abscission layer formation to aid in mechanical harvesting of tart cherries. As with other fruits, ethephon speeds the ripening and subsequent breakdown of cherry fruit, and may contribute to more rapid softening. However, the fruit must be at or beyond the “straw” color before they will respond to ethephon. Green fruit have not yet developed the physiological ability to respond to ethephon.
As in the case of apples, daytime temperatures above 85°F will result in an over response and in tart cherries can result in additional unwanted side effects such as gummosis. Weak or stressed trees should not receive an application of ethephon as gummosis will be even more severe.
Using Ethephon to Manage Fruit Maturity
|1/3 - 2/3 pint/100 gal to promote color developmentMix with 10 ppm NAA/100 gal to slow abscission and fruit drop||15 to 20 days before anticipated harvest||Day: 75-85°FNight: 55-65°FColor development of fruit will not be enhanced when daytime temperatures above 90°F and night temperatures above 70°F||Select blocks for treatment that can be picked and packed over a period of 3 daysTreat each selected block 2 to 3 days apart|
|1/3-½ pint/acre in a dilute spray to synchronize fruit abscission (drop) for mechanical harvest||2 to 3 weeks before harvest||See apples, aboveAt full rate, temperatures above 85°F increases fruit drop, and can cause gummosis||Fruit must be at or beyond “straw” colorDo not apply to weak or stressed treesRate provided is less than labeled rate to minimize risks from higher temperatures|
Preventing Premature Fruit Drop
Some apple cultivars, particularly early ones, are susceptible to pre-harvest fruit drop. Most susceptible cultivars respond to a dilute application of NAA. Ethylene inhibitors can be even more effective than NAA for preventing pre-harvest drop (see table below and the following section).
Using NAA to Prevent Premature Fruit Drop
|Rate of NAA||Timing||Notes|
|10-20 ppmDo not apply as a low volume concentrate spray||No earlier than 7 to 14 days before anticipated harvestTo prevent drop, repeat application no less than 7 days later||Two applications maxMay cause fruit splitting on early season cultivarsNAA will shorten the storage life of fruit|
Delaying Fruit Maturity
Applications of gibberellic acid (GA3) can be used to extend the harvest season of sweet cherries. GA3 (ProGibb) applied when fruit is translucent green to straw color at 16 to 48 grams a.i. per acre delays maturity by 5 to 7 days. The result is larger, firmer fruit with bright green stems and a longer storage life. GA3 also slows color and sugar accumulation, resulting in brighter color at harvest but lower soluble solids.
Aminoethoxyvinyl glycine (AVG or ReTain) blocks the formation of ethylene by plants and can be used to delay maturity and to hold fruit on the tree. AVG can be used as a stop drop with the added benefit of firmer fruit at harvest and a longer storage life. AVG has no direct effect on color development, but allowing the fruit to hang on the trees longer will result in larger fruit with more color development.
Timing is critical. Apply at the label rate 4 weeks before anticipated harvest. AVG acts by preventing the natural abscission process from beginning. However, if this process has already started, AVG applications are not effective. Use at least 100 gallons per acre and spray both sides of the row (no alternate row applications) to ensure good coverage.