Time for Retain application in Vermont orchards

By Terence Bradshaw

Apple harvest is just around the corner with reports of early varieties like Paulared and William’s Pride coming in as ready to pick. The use of plant growth regulators to help with harvest management and improve fruit quality is an important tool in many orchards. ReTain plant growth regulator is used to slow ethylene synthesis in ripening fruit to delay maturity and reduce preharvest drop. Given the dry and hot conditions experienced this summer, drop potential is high, and growers should plan on treating their orchards more often than not. One or two applications may be made at the rate of one pouch (11.7 oz) per acre each. Application 21 to 28 days prior to normal harvest will delay ripening 7-10 days and improve fruit storability. ReTain is especially recommended on McIntosh, and reduced rates (1/2 pouch each application) suggested for Macoun and Honeycrisp. ReTain also improves fruit quality on Cortland and Gala.

Dr. Duane Greene from UMASS recently outlined the following guidelines for ReTain use in 2016:

“Apply ReTain in a sufficient amount of water to ensure that flowers, fruits, and foliage receive thorough spray coverage using calibrated spray equipment. Adjust water volumes based on plant size and spacing. However, excessive spray application volumes resulting in spray runoff will reduce product efficacy.

Avoid applications during the heat of the day. For best results, apply ReTain under slow drying conditions, e.g. early in the morning or at night, in order to maximize adequate absorption.

Do not apply ReTain if rain is expected within 8 hours of application.

Do not apply ReTain to plants of fruit under considerable stress (i.e., heat, water, disease, insect).

Maintain application solution between pH 6-8.

For optimal response, use ReTain with a 100% organosilicone surfactant. Use a final surfactant concentration of 0.05 to 0.1% ( i.e. 6-12 oz surfactant per 100 gallons spray water) in the spray tank. To prevent possible spotting, use the 0.05% concentration when high temperature (in excess of 86°F) weather conditions prevail or are anticipated. Do not use a surfactant concentration greater than 0.1%. To reduce foaming, add the adjuvant last and minimize agitation.

ReTain may be applied in a single application of 1 to 2 packets per acre (or less), or in two applications of 1 packet per acre (or less) each. See the Supplemental Label for additional information: http://bit.ly/2bar9gZ

ReTain has a 7 day pre-harvest interval (PHI) for Apple and Pear.”

Dr. Greene’s presentation slides on PGR use in apples from the 2015 UVM Apple Program/ VTGFA Winter Meeting can be found at: http://www.uvm.edu/~fruit/treefruit/tf_meetings/PGRsVTFGA15.pdf

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