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Trees losing leaves in spring

Tree losing leaves in springAsh trees (as well as maples, oaks and other species) succumb to hardwood leaf diseases known as anthracnoses.  Anthracnoses are often the most conspicuous of the hardwood diseases but are among the least damaging.  Symptoms range from innocuous leaf spots, through blotches and blights of leaves and shoots, to cankers and diebacks of twigs and branches. 

There are different fungi that cause anthracnose in different species of trees.  The fungus overwinters in infected twigs and fallen leaves.  Infection on newly emerged leaves and shoots begins in early spring during cool and wet weather. 

Shortly after infection, irregular water-soaked spots appear on young shoots and leaves.  As the disease develops, leaflets show brown to black blotches or spots, usually from the margins toward the center.  The leaves tend to curl.  Infected leaves often drop prematurely.  Older leaves are more resistant and may only appear spotted.  The disease usually infects the lower portion of the canopy first and then spreads upward. 

A tree may lose a large part of its foliage, but produces a new flush of leaves later in the spring.  The disease does not usually cause permanent damage to the tree, however, repeated leaf loss year after year can weaken trees and predispose them to other pest problems or environmental stresses. 

What you can do:

Rake and remove leaves as soon as they fall so that they do not re-infect healthy leaves remaining on the tree.   Do not compost those leaves but rather dispose of them in garbage bags. Removing leaves in the fall will help reduce the over-wintering population of anthracnose fungi.  Avoid watering the canopy of the tree.

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