Abscisic acid as a potential deciduous fruit tree nursery stock defoliant

Abstract

Abscisic acid (ABA) was tested as a defoliant for nursery trees of 'Bartlett' pear (Pyrus communis L.) and the apple (Malus xdomestica Borkh.) cultivars Imperial Gala, Gibson Golden Delicious, Scarlet Spur Delicious, Law Red Rome, Granny Smith, Braeburn, and Red Fuji. ABA was sprayed once or twice, with 1 intervening week, at 500, 1000, or 2000 ppm. Percentage defoliation was assessed at 1-week intervals for 4 weeks. For all cultivars, two applications of 2000 ppm ABA ranked among the most effective treatments for rapid defoliation; this treatment led to at least 95% defoliation for all cultivars. For many cultivars, however, other treatments caused similar defoliation percentages by digging time. All tested cultivars were effectively defoliated (>80%) by two 1000-ppm applications ABA or one 2000-ppm application. One or two 500-ppm applications effectively defoliated 'Bartlett', 'Gibson Golden Delicious', and 'Law Red Rome'. Nursery managers, therefore, need to consider a range of ABA concentrations and alternative application protocols to obtain optimum benefit from ABA. Although ABA shows promise as a defoliant, it lacks government approval for commercial use.