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Green Ash Tree Diseases

By Carole Ellis ; Updated September 21, 2017
Green ash trees have a large canopy that provides plenty of pleasant shade.

The green ash tree is a hardy, drought-resistant tree that has been heavily planted in urban areas since the onset of Dutch elm disease. This popular shade tree grows tall and has a large canopy, making it a good long-term member of your landscape. There are a number of green ash tree diseases that can slow the growth of your tree or even topple it before its time. Making sure that you are aware of the signs and symptoms of green ash tree diseases will help you keep your tree "happy" and healthy for years to come.

Ash Yellows Disease

Ash yellows is a long-term infection, and it may take several years for you to notice that your tree is in trouble if you do not know the early warning signs. Generally, green ash trees grow 6 to 8 inches each year. However, ash yellows causes a significant loss of vigor, and the trees may only grow 1 inch, or even less. Leaves will pale, becoming yellow and developing fall color and falling far too early. You may start to notice cankers forming on the tree and cracks appearing in the trunk.

There is no certain cure for ash yellows, but you can fertilize the tree and remove the dead and infected limbs to slow or halt the progress of the disease. If your tree continues to founder, then you should have it removed so that the other green ash trees in your area do not also become infected.

Green Ash Anthracnose

Anthracnose is a fungal infection that first manifestsn the form of purple and brown blotches on the leaves of the green ash. These spots may spread and develop creamy, white centers and eventually kill the leaves all together. It tends to infect trees during cool, rainy weather. You should use sterile pruning techniques to remove and dispose of affected branches and foliage since the fungus overwinters on the ground, and fertilize the tree with a nitrogen fertilizer. If you have a green ash that becomes infected every year, you can use a preventative fungicide treatment like chlorothalanil to fortify that tree against reinfection.

Green Ash Verticillium Wilt

Verticillium enters green ash trees through their roots, but the symptoms will appear in the leaves, which will become wilted and brown around the edges. The leaves may also yellow and fall early. There are not currently any chemical controls for verticillium, but you can fortify your tree and attempt to help it fight off the infection by sterile pruning of affected leaves and limbs, watering only when the soil is dry and in the early morning, and fertilizing the tree so that it is able to effectively grow and eventually stop using the root systems that are transporting the wilt.