Plant Growth Regulator Review for 2018

 In 2018 there are 3 materials which are registered for control of pre-harvest drop in apples:  NAA, ReTain and Harvista:

• NAA provides modest drop control because it inhibits abscission, however fruit softening and reduced storage life are likely if warm weather follows application or if harvest is delayed until ripening has been substantially advanced.
• ReTain is a plant growth regulator which inhibits ethylene production in the fruit and reduces pre-harvest drop. It also reduces fruit cracking and fruit greasiness, but it delays the development of fruit red color about 1 week.  Application rates and timings vary by variety.  Applied at varying timings (2-4 weeks pre-harvest) and rates (1/3 to 1 pouch/A) ReTain provides different levels of control of pre-harvest drop and fruit maturity.  Its performance is improved when combined with NAA since the two products work synergistically to reduce fruit drop while the ReTain suppresses the increased production of ethylene triggered by the NAA. 
• Harvista is a newer class of drop control chemical for foliar application, which inhibits the action of ethylene in the fruit and reduces fruit drop.  The AgroFresh Company provides very specific, on-site recommendations for the timing of Harvista recommendations to its customers.

Recent Harvest Management PGR Strategies, Still Under Testing

• Delaying Honeycrisp Harvest:  Single pouch/acre rate of ReTain, 24 days pre-first pick will significantly delay Honeycrisp harvest.
  • Potential to delay harvest 2.5 to 4 weeks. 
  • If you wait long enough, color will eventually develop.
  • Pre-harvest drop was not excessive at 13% in our 2016 Hudson Valley trial, and was not reduced by the ReTain treatment.
  • A second, full pouch treatment 10 days prior to first pick did not have any measurable beneficial effects.
  • Serious soft scald developed in the ReTain treated fruit when rated after 90 days in refrigerated storage in our 2016 trial.  If you try using ReTain on Honeycrisp in this manner, and the fruit is stored, monitor the stored fruit on a weekly basis for soft scald.  Until you gain some storage experience with this program, we can't recommend controlled atmosphere storage.

• "Stacking" Harvista on top of an earlier ReTain application:
  • Several growers in the Hudson Valley have tried this out on McIntosh and Honeycrisp in the last two years.
  •  We have no independent university research results to report on this strategy.
  • Certainly expensive, does it pay off?  Need to see some hard data before it can be recommended.  If you try it, leave an unsprayed control and contact your CCE-ENYCHP fruit specialist to help with evaluation.

McIntosh Harvest Management PGR Recommendations for Eastern New York State

• NAA:  NAA requires 1-2 days to come into effect and will provide a degree of drop control for a period of 7-10 days, although drop control is not always reliable.  In the case where you may need 3-4 days of drop control and long-term storage is not planned, NAA can be useful.  However, since NAA stimulates ripening and can provide unreliable drop control when applied alone, in general the use of NAA alone is not recommended.
• ReTain Timing:  ReTain can be applied 2-4 weeks before anticipated normal harvest.  In general, apply ReTain at 3 weeks before harvest in cool years and at 4 weeks before harvest in hot years.   Growers in the Hudson Valley commonly apply ReTain 4 weeks before the estimated first harvest date, with good success.  The long-range weather forecast through mid-September for both the Hudson and Champlain Valley's predicts warmer that average temperatures for the period.
• ReTain Application Rates:  One pouch of ReTain per acre will give the best drop control but will delay color development by 7-10 days.  A ½ pouch of ReTain will also work and has a less negative effect on fruit color but the control of fruit drop will wear off sooner, perhaps too soon.
• ReTain + NAA:  Dr. Terence Robinson's research in the last several years has shown the best combination of drop control with the least negative effect on fruit color is achieved by splitting a full rate of ReTain into 2 sprays of ½ rate of ReTain each time and including 10ppm NAA in both sprays. Application of the first 1/2 pouch of ReTain per acre + 10 ppm NAA (4oz/100 gal) should be made 3 weeks before normal harvest.  The second application of 1/2 pouch of ReTain per acre + 10 ppm NAA is timed for one week before normal (untreated) harvest.
• Surfactants:  It is critical to include an organosilicone surfactant with ReTain especially when combined with NAA. The organosilicone surfactant, such as Silwet (12 oz. /100 gallons), improves the uptake of ReTain better than other surfactants thus ensuring that sufficient ReTain is absorbed by the leaf to suppress the stimulatory effect of NAA on ethylene production.

Gala Recommendations for Eastern New York State

• Effects of ReTain on Gala:
  • Fruit will remain on the tree an additional 7-14 days.
• Improved fruit size as fruit will increase in size approximately 1% per day
• Reduced stem end cracking and greasiness in 2nd & 3rd picks.
• Aspects of fruit maturity are delayed, and fruit appear to ripen more evenly on the tree.  As a result, is sometimes possible to reduce the number of picks necessary down to one or two.
• ReTain Rates:  Apply a ½ pouch of Retain per acre.   The 1- 2 pouch rates of Retain are almost never recommended since Retain at higher rates has a very strong negative effect on Gala color development.  Our trial in 2016 showed that Gala treated with these high rates will eventually color if harvest is delayed 2.5-3 weeks.
• ReTain Timing:  Apply 2-3 weeks before expected first harvest. 
• Surfactants:  It is critical to include an organosilicone surfactant with ReTain.  The organosilicone surfactant, such as Silwet (12 oz. /100 gallons), improves the uptake of ReTain better than other surfactants.

Honeycrisp Recommendations for Eastern New York State 

• Honeycrisp is a low ethylene producing variety that has very uneven ripening but can have significant pre-harvest drop in some years.  The use of retain is recommend in blocks that have had a pre-harvest drop problem in the past.
• ReTain Timing:  Apply three weeks before expected harvest. 
• ReTain Rates:  Apply 1/3 of a pouch/acre rate of Retain on Honeycrisp.  Champlain Valley growers may want to consider a ¼ pouch rate and avoid blocks with a history of soft scald.
• Surfactants:  It is critical to include an organosilicone surfactant with ReTain.  The organosilicone surfactant, such as Silwet (12 oz. /100 gallons), improves the uptake of ReTain better than other surfactants.

 Harvista Observations and Recommendations

• Pre-Harvest Fruit Drop Control.
• Safe delay of harvest for additional color and fruit size development.
• Maintenance of fruit firmness before and/or after harvest (storage benefits are short term).
• Slowed starch conversion.
• Delayed and reduced incidence of water core.
• Greater consistency in maturity for improved storage performance.
• Fewer pick dates required for multiple-pick varieties.
• Recent research has demonstrated a reduction in Soft Scald in Honeycrisp.

Harvista Timing & Rates:  The general timing range is 3-14 days pre-harvest.  Please contact AgroFresh technical support for specific guidance.