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Ash anthracnose

During the week of May 17th , many ash trees in central Minnesota dropped leaflets in great numbers after more than two weeks of cool, rainy weather. This disease is called ash anthracnose and it is caused by a fungus, Gnomoniella fraxini, one of the most common foliar disease of ashes in the United States.

Round to irregular blotches appear along margins and midribs of leaflets. They are greenish-brown at first but turn brown with age. Sometimes, infected leaflets curl and drop before the blotch symptoms are well developed. Later during the season, numerous small, round lesions with gray centers and purple-brown margins may develop on leaves remaining on the tree. Small anthracnose cankers may occur on twigs of trees severely defoliated for several years. They may cause dieback.

Rake and burn or destroy fallen leaves and twigs. If chemical control seems necessary, apply benlate,
thiophanate, or mancozeb.