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Earlier this spring I received some calls from homeowners who were concerned that they might have emerald ash borer (EAB) because the ash trees weren't leafing out. They realized that ash are the last to leaf out in the spring but because of the early spring the ash should leaf out also, but they didn't. Several of the Master Gardeners received calls about green beetles thinking they were the EAB.

There are several green insects that may be confused with the emerald ash borer. The adult is a slender insect about one-third to one-half inch long. It is widest just behind the head, gradually tapering back to the abdomen. It is a bright irridescent green to copper green color, often with a copper colored area behind the head. Underneath the wings is a purplish magenta color.

EABs generally have a one year life cycle, although that can be extended to two years in a vigorous host. They overwinter as fully grown larvae in chambers constructed under the bark of ash trees. The distinctly segmental larva is relatively easy to locate by peeling back the bark of the infected tree. The larva is soapy white and the segments resemble tiny bells end to end. The head is copper colored and has a streak the entire length of the segments. They pupate in early spring and emerge as adults, leaving characteristic "D" shaped exit holes.

If a tree is suffering from the infestation with EAB, the trees canopy will appear thin with few or no leaves. Eventually dead branches will be noticed. Cracks and "D" shaped exit holes can be found in the bark or infected trunks, and woodpeckers may be noticed frequently visiting infected trees to feed on the larva.

In contrast, trees infected with ash anthracnose will have dark brown to black water-soaked blotches on leaves and young shoots. These leaves are often distorted and curled around the infected area of the leaf. Sometimes the infection can result in leaf drop, and in severe cases, a complete loss of the first flush of leaves can result. Infection is often most severe in the lower and inner branches of the tree where high humidity favors fungal growth. It is very common in cool wet spring weather.

Ash Anthracnose is considered a minor stress to a tree. A mature vigorously growing tree can tolerate complete loss of leaves for two to five years.

Reducing other stresses on the ash tree throughout the growing season can help the tree recover. Simple activities like watering trees during periods of drought, mulching the soil at the base of the tree to reduce competition with turf grass, and avoiding wounding the tree with lawn equipment, can keep the tree strong. Removing infected leaves at the end of the growing season can help reduce the amount of fungi that survives from one season to the next, although some fungi often survives within the tree canopy.

Although there are fungicides that will prevent Ash Anthracnose, it must be applied early in the growing season to protect young emerging leaves and shoots. Fungicides are only recommended in trees that have suffered severe leaf loss due to the disease several years in a row. Homeowners should have a certified pesticide applicator treat mature trees.

Parts of this article were taken from research done by Michelle Grabowski, UMN Extension Educator and Jeff Hahn, UMN Extension Entomologist.

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