Effects of adjuvants on distribution and rainfastness of captan sprays on apple leaf scars to control European canker

Abstract

Autumn leaf scars are an important pathogen infection site for European canker on apples Trials were undertaken to evaluate the effects of adjuvants on spray coverage of new leaf scars and determine if adjuvants could (1) impart any significant rainfastness to protectant captan sprays and (2) provide any redistribution of captan during a rain event postleaf drop Retention on fresh leaf scars was increased with the use of organosiliconelatex sticker adjuvants only Rain had little effect on spray residues but these adjuvants could improve rainfastness of captan due to their effects on spray retention Retention on stem wood and around leaf nodes was increased by up to sevenfold with the use of superspreadertype adjuvants due to redistribution of spray runoff from leaves High initial deposits resulted in postrain residues on leaf scars threefold higher than a captan spray alone Redistribution of captan onto exposed leaf scars in rain appears likely with these adjuvants