Effects of Daminozide, Paclobutrazol, and Uniconazole Treatments on `McIntosh' Apples at Harvest and Following Storage

Abstract

Foliar daminozide (DZ) applications to `McIntosh' apple trees (Malus domestics Borkh.) increased fruit color, reduced preharvest drop, resulted in greater firmness at harvest and after air storage, delayed starch hydrolysis, and reduced fruit ethylene production at harvest and after storage. Foliar paclobutrazol (PBZ) reduced preharvest drop and flesh firmness loss if applied within 5 weeks after full bloom (WAFB). Later applications had no effect. PBZ did not influence the progress of starch hydrolysis or ethylene production at harvest but reduced poststorage ethylene production in one season. Stem-cavity browning and brown core were increased by PBZ applied at 5 and 9 WAFB in 1987. In 1988, fruit soluble solids content (SSC) was reduced by a double application of PBZ and by uniconazole (UCZ). UCZ had little effect on `McIntosh' fruit other than the reduction in SSC. PBZ applications were less consistent in their effects than DZ. Chemical names used: butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); ß-[(4-chlorophenyl) methyl]-α- -(l,l-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol); ß-[(4-chlorophenyl)methylene]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (uniconazole).