Green ash trees are susceptible to a widespread pest called the emerald ash borer. This pesky insect has caused havoc for all varieties of ash trees throughout Michigan, Ohio, Illinois and other parts of the Midwest. The emerald ash borer along with ash yellows disease and verticillium wilt can cause extensive problems with the ash trees in your landscape. The green ash tree must be inspected often to prevent infestation of these harmful ailments, along with heart rot and anthracnose, which also affect green ash varieties.
Inspect ash trees often for D-shaped exit holes in the bark. The adult beetle will leave this mark when leaving the tree. Peel away a piece of bark and inspect the tree for S-shaped tunnels that snake around the tree. Notify the local state extension service if evidence of the emerald ash borer is found in your landscape. There is not a cure for this insect and it does not react to insecticides. Prevent the emerald ash borer by following your state's recommendations on quarantining along with providing the essential nutrients to keep your ash trees healthy. Provide adequate water. A drought-stressed tree will be more inclined to harbor these insects than a healthy tree.
Diagnose ash yellows disease early. This disease is caused by the spread of wall-less microbes that invade the tree's vascular system. Inspect trees for a rapid decline in radial growth and leaves that are a lighter green than normal. The leaves will often be smaller in size compared to a healthy tree. Remove trees with extensive damage and increase water to infected trees. This is an incurable disease, but increased water intake will allow the tree to live for five to 10 years.
Inspect the tree for verticillium wilt. This soil-borne fungus attacks woody ornamental trees. Look for leaf curling, drying or an abnormal red or yellowing of the leaves. Control the fungus, maintaining a strict watering schedule. Remove dead and weak branches to promote healing, although the disease is untreatable.
Inspect green ash trees for anthracnose. Anthracnose is caused by a fungal infection that infests the leaves, buds and twigs of the green ash tree. It develops in mild temperatures, especially with a high May precipitation rate. Rake and destroy fallen leaves in the autumn to prevent anthracnose. Apply a fungal preventive spray three times per year according to the package directions to rid plants of this fungus and prevent future infestations.
Prevent heart rot by removing severely damaged or infested green ash trees. Heart rot is brought on by a fungus and thrives in mature or over-mature trees. Prevent heart rot with careful pruning. Avoid pruning wounds, which allow the fungus to enter the tree. Remove broken branch stubs from the tree.