Consequences of environmental stress on oak: predisposition to pathogens

Abstract

Mortality of stressed trees results usually from lethal attacks by opportunisitc pathogenic organisms that successfully invade and colonize stress-weakened trees. Oak trees are predisposed to these organisms by defoliation, primarily from insects, but also by fungi and late spring frosts, and by drought. There is some evidence that injury from extreme winter temperature fluctuations also can act as a predisposing stress. Fungal organisms, such as Armillaria spp in the root system, Hypoxylon sp on the bole, and a number of fungi that invade branch systems, and insect borers, such as Agrilus spp, take advantage of changes induced by stress and successfully attack and kill trees.