Crop Load Management of Apple by Chemical Fruitlet Thinning, Preharvest Drop Management, and Investigation of Abscission Physiology
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Abstract
New crop load management strategies are required for apple trees to thin fruit and delay preharvest fruit drop (PFD). The efficacy of the chemical thinners 1-aminocyclopropane-1-carboxylic acid (ACC) alone, and abscisic acid in combination with 6-benzyladenine was determined on 'Gala' apples. The efficacy of ethephon and ACC was determined when fruitlets were 15-25 mm, outside the traditional thinning window. Abscisic acid and ACC produced acceptable fruit set, crop load, and quality in one year and ACC applied at 15-25 mm was effective only at 15-16 mm. In another study, ‘Honeycrisp’ was used to evaluate the efficacy of aminoethoxyvinylglycine, naphthaleneacetic acid, and foliar sprays of boron and magnesium on PFD. Fruit drop was reduced 27% by naphthaleneacetic acid and 35% by aminoethoxyvinylglycine while maturity was delayed. Cultivars prone and not prone to PFD were compared for seasonal xylem function in the fruit, which was lower in the cultivar prone to PFD.