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Ash Anthracnose (06/06/19)

Conditions this spring were ideal for ash anthracnose to develop in ash trees, leaving blotchy, distorted leaves and partial to complete tree defoliation.

Conditions this spring were ideal for ash anthracnose to develop in ash trees, leaving blotchy, distorted leaves and partial to complete tree defoliation.  Ash anthracnose is caused by a fungus which infects leaves during cool, moist conditions.  It is common throughout North Dakota.  Many of the trees that have been defoliated this spring will grow new leaves and appear to completely recover.  Trees that are already severely stressed may have more difficulty.

Although ash anthracnose is caused by a fungus, treating with a fungicide now will have no effect on the infection because it is already inside the leaves.  Ash anthracnose is only a serious problem when a tree is repeatedly defoliated over several years or if a tree is already suffering from other severe stresses.  Trees may be helped by a light fertilizer application (1-3 pounds of nitrogen per 1000 square feet of ground surface).

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Lezlee Johnson

North Dakota Forest Service

Forest Health Manager

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