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
Apple
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 requires 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.
Tart Cherry
In tart cherries, ethephon speeds the process of fruit abscission (fruit drop). This allows for a synchronization of fruit drop for mechanical harvesting. It also 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.
Because daytime temperatures in the Intermountain West routinely exceed 85°F in the weeks leading up to tart cherry harvest, growers often reduce the rate by half, which seems to give the beneficial effect of synchronized fruit abscission but lessens the risk of harmful side effects. All of the fruit should be at the straw color before ethephon application. See the table below for rates and other information.
Using Ethephon to Manage Fruit Maturity
| Rate | Timing | Temperature | Notes |
|---|---|---|---|
| Apple | |||
| 1/3 - 2/3 pint/100 gal to promote color development Mix with 10 ppm NAA/100 gal to slow abscission and fruit drop |
15 to 20 days before anticipated harvest | Day: 75-85°F Night: 55-65°F Color 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 days Treat each selected block 2 to 3 days apart |
| Tart Cherry | |||
| 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, above At full rate, temperatures above 85°F increases fruit drop, and can cause gummosis |
Fruit must be at or beyond “straw” color Do not apply to weak or stressed trees Rate 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. However, NAA will not delay fruit maturity, may shorten shelf life, and the stop drop activity tends to be short-lived.
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 is a stronger stop drop than AVG, with the added benefit of delayed maturation, which can reduce stem-end cracking, improves fruit firmness and 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 as 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. 1-MCP (Harvista™) acts by blocking ethylene response and can be used to both reduce preharvest drop and improve post-harvest shelf life.
Using NAA, AVG, or I-MCP to Prevent Premature Fruit Drop
| Rate of NAA | Timing | Notes |
|---|---|---|
| NAA | ||
| 10-20 ppm Do not apply as a low volume concentrate spray |
No earlier than 7 to 14 days before anticipated harvest To prevent drop, repeat application no less than 7 days later |
Two applications max May cause fruit splitting on early season cultivars NAA will shorten the storage life of fruit |
| AVG (ReTain) | ||
| 1 to 2 pouches per acre, dilute spray | 21 to 28 days prior to anticipated start of harvest for single application | May be a split application (one pouch per application) with the first at 28 days before harvest, and the second 7 to 14 days later. |
| I-MCP (Harvista) | ||
| 48 to 242 oz. per acre, maximum of 242 oz per acre per season | 21 to 28 days prior to anticipated start of harvest for single application | 3 to 21 days prior to anticipated harvest |
Delaying Fruit Maturity
Sweet Cherry
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.
Conclusion
PGRs can be a useful aid in managing orchards, but require careful timing, mixing and application. Sloppy techniques will give disappointing results and will waste time and money. With careful record keeping, it will be possible to track from year to year which rates, materials and environmental conditions produce acceptable results on each cultivar.