Further studies on chemical defoliation of deciduous nursery plants

Abstract

In experiments with cultivars of apple, pear, plum (European and Japanese), peach, almond, apricot, and cherry the defoliation effects were measured of concentrations of potassium iodide (KI), bromodine, DEF (S,S,S-tributylphosphorotrithioate) and a bromodine/ethephon ((2-chlorethyl) phosphonic acid) mixture, applied as either single or double sprays. Double sprays and higher concentrations were more effective than single sprays and lower concentrations but the most effective chemical differed between species. In further experiments the effects were measured of pre-spraying with the growth retardant SADH (succinic acid -2, 2-dimethylhydrazide) or the auxin transport inhibitor TlBA (235-triiodobenzoic acid) followed by selected defoliants. Pre-spraying with SADH followed by either potassium iodide or bromodine significantly increased leaf fall on apricot but not Japanese plum or almond. Pre-spraying with TIBA followed by ethephon or DEF significantly increased leaf fall on apple and almond but not pear or apricot.