Since 1990, ash trees have been in decline across many Northeastern and Midwestern states. There is no single cause, no one disease that is killing ash trees. Current scientific research indicates that multiple factors are involved, including insect pests, environmental factors and disease.
One of the biggest dangers to ash treas comes not from disease, but from an insect pest: the emerald ash borer (agrilus planipennis). This destructive insect was introduced to the United States from its native Asia in the mid-1990s. The emerald ash borer lays eggs under the bark of the tree. Larvae eat away the soft layers of wood that act as the tree's "blood vessels," transporting water and nutrients, weakening and eventually killing the tree.
Signs of Emerald Ash Borer Infestation
The first sign of emerald ash borer infestation might be the presence of woodpeckers. If you start to see woodpeckers, or the distinctive holes they leave in your ash trees, check for the other signs of infestation: the leaves will turn yellow, and some will die and fall off, leaving the tree looking bare; branches die starting at the top and progressing downwards; holes appear in the bark where the insects have eaten their way out of the tree; sections of bark may fall off the tree to reveal tunneling; you may even see the larvae or adult insects.
If caught early, emerald ash borer infestation can be treated by giving the affected tree extra water and fertilizer to help it recover from the damage, and with insecticides. Insecticide treatment should only be done by professional arborists. Badly infected trees must be removed and the wood either chipped or burned. It's best to replace the tree with a different species to stop the problem from coming back.
Ash Yellows Disease
Not all ash tree disease is caused by the emerald ash borer. Ash trees are also being attacked by a disease called "ash yellows." Ash yellows disease is caused by fungus-like microbes that infect the tree and disrupt its ability to take up and distribute water and nutrients. White ash and green ash species are most commonly affected, but all ash species are at risk.
Symptoms and Treatment
Symptoms of ash yellows disease include very slow or no growth; small, pale-colored leaves; very early yellowing in fall. Only a laboratory test can confirm for sure if a sickly ash tree has ash yellows disease, and there is no known treatment or cure. Diseased trees must be removed, and should be replaced with a different species of tree.