AN UPDATE ON PREHARVEST DROP CONTROL OF APPLES WITH AMINOETHOXYVINYLGLYCINE (RETAIN)

The effectiveness of aminoethoxyvinylglycine (AVG) as a preharvest drop control agent on apples has been confirmed by many researchers over the past decade. Effectiveness increases linearly with increasing concentration. An application 2 to 3 weeks before the anticipated start of harvest is most effective to retard preharvest drop during the normal harvest period and for a period of time after. Once applied, it requires about 10 days for AVG to start to retard preharvest drop. The silicone based surfactants Silwet L-77 and Sylgard 309 are required for best preharvest drop control. If rain occurs within 8 hours of application, the effectiveness of AVG will be reduced. However, if Silwet L–77 or presumably Sylgard 309 are included when AVG is applied, rain, even if it occurs within 1 hour of application, will not reduce the effectiveness of AVG. A reduction in drop control may be observed if the application is concentrated more than 2 times. Drop control is observed when AVG is applied to either the leaves or the fruit but the greatest control is achieved when both leaves and fruit are thoroughly covered. AVG retards ripening and delays the onset of the ethylene climacteric, slows the loss of flesh firmness and delays the hydrolysis of starch to sugar. Reduced red color is associated with delayed ripening rather than an inhibition of red color development. AVG has no direct effect on fruit size but because it allows the fruit to remain on the tree for a longer period of time, larger fruit are frequently harvested from AVG-treated trees.