Evaluation of GA4+7 plus 6-Benzyladenine as a Frost-rescue Treatment for Apple

Freeze events during bloom can be a relatively frequent occurrence in many apple (Malus ·domestica) production areas in the United States that significantly reduce orchard productivity and profitability. This study investigated the potential for a proprietary mixture of gibberellin A4 D A7 and 6-benzyladenine (GA4D7 plus 6-BA) to increase fruit set and cropping of apple following freeze events at three locations across the United States during bloom in 2012. GA4D7 plus 6-BA increased fruit set in two of five experiments, and increased fruit number and yield per tree in three of five experiments. GA4D7 plus 6-BA increased fruit set and yield of ‘Taylor Spur Rome’ following freezes on two consecutive days during bloom when the minimum temperature reached 23.9 and 28.4 F. Fruit set was increased due to a stimulation of parthenocarpic fruit growth. Using locally obtained market prices, GA4D7 plus 6-BA treatments increased the crop value of ‘Taylor Spur Rome’, ‘Ginger Gold’, and ‘Jonagold’ by $3842, $977, and $6218 per acre, respectively. Although GA4D7 plus 6-BA application(s) after a freeze increased fruit set and cropping in some instances, tree yields were well below the average yields previously obtained in the test orchards.