Effects of Gracillariid Leafminers on Apple Tree Growth and Production1

Abstract

Infestations of Phyllonorycter crataegella (Clemens), the apple blotch leafminer (ABLM), averaging more than two mines per leaf caused premature fruit drop from ‘McIntosh’ apple trees in eastern New York and reduced fruit set the following season. Infestations of ABLM averaging more than four mines per leaf reduced the size of ‘Red Delicious’ apples. In western New York, varying populations of P. blancardella (F.), the spotted tentiform leafminer, had little effect on the growth or production of ‘Idared’ or ‘Rome Beauty’ cultivars during the initial year of infestation, but reduced fruit set and consequent production during the following season. Apparently, the second generation of larvae caused more damage than the first.