Stress Related to Diseases

Summary Diebacks and declines are diseases triggered by the predisposing effects of biotic or abiotic stress factors and culminated by the attack of organisms of secondary action. In the forest, the primary stress factors are insect defoliation and extremes of moisture and heat. Of the many stresses in urban situations, drought is probably the most important. Organisms of secondary action are facultative parasites and are common inhabitants of natural ecosystems. Often they assume greater importance in urban environments than in natural habitats. Control of dieback and decline diseases usually requires preventing or reducing the effects of the stress agents rather than controlling the secondary-action organisms that cause mortality.