How Will Landscape Plant Diseases Respond to the Drought of 1999?
by John Hartman, Extension Plant Pathologist In contrast to the drought effects on diseases of annual crops discussed in the accompanying articles, drought effects on diseases of perennial plants can be very dramatic. In the case of trees and shrubs or fruit crops, the drought has not only affected the pathogen but also the physiology of the host from one year to the next. Host plant condition affects its reaction to disease. Woody plants. Most of us are familiar with wilting and leaf scorch symptoms associated with dry weather. This past year, leaves of drought-stressed plants closed their stomata which reduced their rate of photosynthesis. Reduction in photosynthesis may not kill a tree or shrub, but it means fewer carbohydrates are made and stored for future use. In the landscape, seedlings and recently transplanted trees and shrubs were at greatest risk because they lacked extensive root systems. With drought, there are some fungal diseases of landscape trees and shrubs that often
