Use of alpha-naphthylacetic acid in ovary thinning and preharvest fruit drop reduction in apple trees

Abstract

Chemical thinning of apple ovaries in intensive orchards is highly relevant. This farming practice reduces manual labour, decreases  the  fructification  interval and improves apple quality. Growth regulators, including alpha-aphthylacetic acid,  also  reduce preharvest fruit drop allowing for an optimal harvest capacity. The research aimed to study the impact of different alpha-naphthylacetic acid application rates on ovary thinning  and preharvest  fruit drop. Assays were conducted in 2019—2020  in a  leached-chernozem experimental apple orchard of the Michurin Federal Research Centre  in Tambov Region. Assay 1 studied the treatment impact on apple tree thinning at rates 100, 200, 300 and 400 ml/ha in 8—12 mm fruits, assay 2 (treatment 2 weeks prior to expected harvest) —  on reducing preharvest apple drop at rates 200, 300 and 400 ml/ha. The treatments significantly reduced the number of ovaries in the Zhigulevskoe/62-396 cultivar and increased mean apple fruit weight. Such increase was an important yield-rising factor in the 300 and 400 ml/ha treatments. Alpha-naphthylacetic acid treatments in 8—12 mm fruits had a significant lowering impact on total leaf nitrogen content. The treatments also induced a significant reduction in preharvest apple fruit drop, with the best effect at rate 300 ml/ha. No explicit impact of alpha-naphthylacetic acid on fructification interval was observed in the study period.