Chemical defoliation of deciduous nursery plants

Abstract

Peach seedlings were pre-sprayed with the growth retardant SADH (Succinic acid-2,2-dimethylhydrazide) at nil, 2000 or 4000 p.p.m. followed by one or two applications of the defoliant ethephon . ((2-chloroethyl) phosphonic acid) in either March or April at nil, 100, 200, 300, or 500 p.p.m. Leaf drop was increased by SADH and ethephon. Two applications of ethephon were better than one and April sprays were better than March sprays. Phytotoxic effects occurred with ethephon at 500 p.p.m. In a second experiment cultivars of a range of species were sprayed with the defoliants ethephon and DEF (S,S,S-tributylphosphorotrithioate) at various concentrations. In general DEF was the more promising chemical with good results on apples, pears and cherries. Neither compound was successful for peaches, apricots and Japanese plums.