Harvest Management and Pre-Harvest Fruit Drop : New England Tree Fruit Management Guide : UMass Amherst

J. Clements (UMass), D, Greene (UMass), and R. Moran (UMaine)

There are three plant growth regulators for pre-harvest drop control. One is NAA, sold as several different products, another is AVG, sold as ReTain (Valent USA Agricultural Products), and the third is 1-methylcylopropene sold as Harvista^TM (Agrofresh). The three differ in mode of action and timing of application. NAA is typically applied just once before the onset of fruit drop and lasts for about one week before its effect is gone. ReTain is typically applied 2-3 weeks before anticipated harvest, has long lasting drop control if applied under favorable conditions, and repeat applications can be made to extend the period of time apples will remain on the tree. Harvista can be applied 3 to 21 days before harvest and requires specialized equipment (contact Agrofresh). Both ReTain and Harvista will slow fruit ripening. For an excellent summary/discussion of uisng apple PGR's for drop control, see this Penn State University article: Apple PGRs - Prevention of Preharvest Drop in Apple Orchards.

Application details for NAA (PoMaxa, Fruitone-L, Refine 3.5 WSG, Refine 3.5L)

Rates of 10 ppm are usually effective, however, up to 20 ppm can be used.
PoMaxa, Fruitone L rates equivalent to 20 ppm are 8 to 32 fl. oz. per acre depending on dilute tree-row volume (8 fl. oz. per 100 gals.). Refine 3.5 WSG rates are 8 to 32 oz. per acre for the 20 ppm rate. REI is 48 hours and PHI is 2 days.
Good coverage at dilute application is preferred.
Apply just as apples starts to loosen; apply too early and drop control will be limited; apply too late, and drop will have already started.
Drop control can last for 7-10 days; sometimes two applications (at 5-7 days apart) can extend that to 14 days.
NAA application can result in accelerated fruit maturity and fruit softening. Storage potential will be limited.

For more information: Getting the most out of that "old" stop drop: NAA (http://healthyfruit.info/hf090517ved818.html#h)

Application details for ReTain

Note that the ReTain label gives very specific instructions depending on intended use -- read it!

General use guidelines for ReTain include:

Application timing will depend on how you want to manage the harvest. Application 4 weeks before the start of harvest will delay ripening in the "first pick" apples, but will wear off by the end of harvest. Application at 7 days before harvest will have little impact on ripening in the "first pick", but will slow ripening in the apples that would be harvested last.
Apply 21 to 7 days before anticipated harvest (7 day PHI). REI is 12 hours.
Use one pouch (or less) per application; two applications are allowed.
On Honeycrisp and Gala, consider using reduced rates -- early application of ReTain can inhibit color development on these varieties.
Use an organosilicone surfactant at a concentration of 0.05 to 0.1% (6.4 to 12.8 oz surfactant per 100 gallons water) with ReTain, do not apply when temperature exceeds 85 degrees F.
Dilute applications are recommended, up to 2 X concentration.
Avoid application when rain is expected within 12 hours.
Do not apply to stressed trees.
Avoid application with calcium chloride as phytotoxicity has been observed.

ReTain can be combined with NAA to prolong drop control. For McIntosh, apply Retain at the full rate with an NAA product at 10 ppm (4 fl. oz. per 100 gals. dilute equivalent) at three weeks before first harvest. A second application may be needed to prolong drop control of McIntosh.

For more information: Double Applications of ReTain® to provide longer fruit drop control compared to the standard single application ReTain

ReTain Plant Growth Regulator Technical Manual

Application details for Harvista^TM

Applied at a rate of 48 to 242 fl. oz.
Do not add any water to the container.
Do not allow product to contact any copper.
Drop control can last for 7-10 days.
Maturity will be halted upon application, eventually wearing off.