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Where have all the ash leaves gone?

Ash leaflets cover the ground

It looks like fall in some parts of Moorhead, Barnesville, Dilworth, and Fargo. Many people have observed streets, sidewalks, and yards covered in ash leaves. The leaf drop is caused by a fungus commonly known as ash anthracnose. Ash anthracnose is common every year, however, incidence and severity is greater this year due to ideal environmental conditions.   

Ash anthracnose survives the winter on infected plant tissue such as leaves, petioles, twigs, and fruit. During spring and summer when the weather is cool and wet spores are produced on infected tissue. The spores are spread by wind and splashing rain to succulent new growth where new infections occur. The classic symptoms of ash anthracnose are irregularly shaped leaf spots that are brownish in color and leaf spots with purple halos. Leaf spots with purple halos seem to be most common this year. Severe leaf infection can cause extensive defoliation.

Ash anthracnose is most severe on the lower and inner portions of trees where humidity and moisture levels are highest. Generally, ash anthracnose does not cause permanent damage to healthy, established trees. However, a tree may be weakened by severe defoliation several years in a row which could lead to branch dieback and attack by opportunistic pests like boring insects or canker causing fungi. 

Cultural control measures such as watering during drought periods, mulching, and fertilizing (if determined to be necessary by a soil test) will help reduce tree stress. There are fungicides labeled for control of ash anthracnose, however they are not recommened unless a tree has been repeatidly defoliated. More information on ash anthracnose can be found here

If you have questions about ash anthracnose please call Randy Nelson at the University of Minnesota Extension office, Clay County at 218-299-7338, 1-800-299-5020, or by email nels1657@umn.edu.