For growers interested in using these products on Early/Mid-Season apple varieties, now is the time to consider applying them.  Think high value varieties such as early season Honeycrisp.

As apples mature they produce the hormone ethylene.  Ethylene induces stem loosening which results in pre-harvest drop of apples.  Luckily there are several tools that when applied at optimal times can aid in the management of pre-harvest drop of apples.

*Prior to the application of any product though, remember to read and follow the product label, because the label is the law.

 

Plant Growth Regulator Options for Apple Harvest Management

Active Ingredient: AVG (aminoethoxyvinylglycine)

ReTain 

This product slows starch disappearance, fruit softening, stem loosening and red color development.

Benefits include:

Expansion of the harvest window by minimizing pre-harvest drop and retaining fruit firmness.
Enhancement of fruit size since fruit are given more time to hang onto the tree.
Color enhancement due to exposure to improved weather for fruit coloring (warm sunny days and cool nights).

Application Timing: For maximum efficacy ReTain must be applied 4 weeks prior to harvest.

Single Pick Varieties

For single pick early season varieties, establish the ‘usual’ harvest time for the variety, and if the season is running early adjust the date earlier (accordingly).  Once an accurate estimated harvest date is established count back four weeks.  This timepoint plus 7 days is the spray window for ReTain for that variety.

Calculate the spray timing for later season, single pick varieties in a similar way.  However, later varieties generally do not need harvest date adjustment due to seasonal variation in the same way early season varieties do.

Multiple Pick Varieties i.e. Gala and Honeycrisp

Spray timing for these varieties is 7 to 14 days prior to harvest/first pick.  Note that ReTain will not affect the first harvest/pick but will provide stop drop control for later season picks.

Variety Response to ReTain and Rate:

*When applying ReTain be sure to include 100% Organosilicate surfactant @ 12 ounces/100 gallons.
*Ensure there will be 6 hours of drying time after the application.

 

Active Ingredient: 1-MCP (1-Methylcyclopropene)

Harvista

Much like ReTain this product slows starch disappearance, fruit softening, red color development and pre-harvest drop.

Application Timing: It should be applied within 3 days prior to harvest, much closer to the time of harvest than a ReTain application.  This product is a bit more complicated to use in that it must be applied via a proprietary in-line injector system.

 

Active Ingredient: NAA (naphthaleneacetic acid)

NAA (Multiple Formulations)

This product provides what is considered a rescue treatment for control of fruit drop.

Application Timing: Optimum timing of spray is a couple days prior to harvest, when the first fruit begins to drop.

One application of 10 ppm NAA will provide 7-10 days of drop control.
A two-part spray of 10 ppm, one a couple days prior to harvest and a second 5 days later will provide 10-14 days of drop control.
Keep in mind it takes ~2-3 days for the sprays to take effect.

*Apply with a nonionic or organosilicate surfactant.
*Spray when the temperatures are in the mid 70’s.  If the temperature is too hot, fruit ripening can be accelerated.

 

Table 1. A quick comparison of compounds registered as stop drops.

Parameter	ReTain	Fruitone, PoMaxa, or Refine	Harvista
Active Ingredient	AVG	NAA	1-MCP
What Is Blocked	Ethylene production	Stem loosening	Ethylene action
Drop Delay (Approximate)	10–14 days	5–7 days	10–14 days
Fruit Ripening	Slowed	Advanced	Slowed
Fruit Color	Delayed	No effect	Somewhat delayed
Fruit Softening	Delayed	No change or advanced	Delayed
Applied (Relative to Drop)	2-4 weeks before	Just prior to	Just prior to
Rescue Option?	No	Yes	Yes
Days to Take Effect	>7	~2	~2
Split Sprays Helpful	Yes	Yes	Not applicable
REI	12 hours	48 hours	4 hours
PHI	7 days	2 days	3 days

Cited from 2024-2025 Penn State Tree Fruit Production Guide page 79.

 

For additional details on utilizing plant growth regulators for harvest management read:

2025/2026 New Jersey Commercial Tree Fruit Production Guide Chapter 10.
https://njaes.rutgers.edu/pubs/publication.php?pid=e002

Apple PGRs – Prevention of Preharvest Drop in Apple Orchards – Production and Harvesting – Fruit – Forage and Food Crops (psu.edu)