Leaf Spot Disease of Trees and Shrubs

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Even the most conscientious and hardworking gardener is likely to encounter leaf spot problems on trees and shrubs. The seemingly sudden appearance of brown or black blotches on leaves and defoliation are common occurrences. It is unlikely that most homeowners will make it through a season without at least one problem with a leaf spot pathogen.

Symptoms

Symptoms of leaf spots vary depending upon the causal agent. Although leaf spots can be caused by air pollutants, insects, bacteria et al., most are a result of infection by pathogenic fungi. Once into the leaf, the fungi continue to grow and leaf tissue is destroyed. Resulting spots vary in size from that of a pin head to spots that encompass the entire leaf. Dead areas on the leaves are usually brown, black, tan or reddish in color. Occasionally the necrotic areas have a red or purple border.

Partial to complete defoliation may occur under favorable conditions for the causal fungus.

Prepared by: David B. Schroeder, Cooperative Extension Plant Pathologist, University of Connecticut