Mechanical Blossom Thinning of 'GoldRush' / M.9 Apple Trees with Two String Types and Two Timings

Abstract

'GoldRush' / M. 9 NAKBT337 apple trees [Malus× domestica(Borkh.) Mansf] were mechanically blossom thinned at either pink or full bloom bud stages, using a Darwin mechanical thinner with either of two different string attachments. Thinning treatments removed entire blossom clusters, reduced flower number on remaining spurs, removed 15-29% of the spur leaf area of persisting spurs, and reduced initial fruit set when compared to the hand thinned control. Mechanical blossom thinning treatments reduced hand thinning time, crop load and yield per tree, but had no effect on mean fruit weight at harvest. Fruit size distribution was unaffected by thinning treatment. Fruit firmness from mechanically thinned trees increased when compared to the control. No differences were observed in soluble solids concentration or acidity between fruit from hand thinned control and mechanically blossom thinned trees. Thinning at pink increased 2013 return bloom when compared to the hand-thinned control and to treatments applied at full bloom. String type and timing were not significant factors to explain the differences in efficacy that have been observed in our previous trials.