Other Insect Problems Associated with Ash Trees
There are other insects that can be found under the bark of ash tress. It is important to be able to identify native insects found in dead and dying trees from the Emerald Ash Borer.
Eastern Ash Bark Beetle is found on dead ash trees. It leaves small round exit holes and the larvae leave distinct galleries that run perpendicular to the wood grain.
A number of native species of Agrilus beetles in Wisconsin attack birch, honeylocust, oak, and other trees and shrubs. Some of these native species include the Bronze Birch Borer and the Two-Lined Chestnut Borer. There is one native species, Agrilus subcinctus, that can infest ash trees. This uncommon species is about half the size of EAB and prefers to infest small branches and twigs.
Ash Borer is a native clear wing moth that can kill smaller trees. This moth leaves round pencil sized holes in the trunk. Unlike EAB, this insect removes frass from its larval galleries. The frass tends to pile up around the base of the tree and looks like a small pile of sawdust. Look for pupal case or exit holes on trunk or larvae in the wood.
The red headed ash borer is a native long-horned beetle. This borer attacks stressed or dead hardwood trees, including ash trees. Exit holes are round and ~1/4″ in diameter.
Distinct, globular galls can often be seen in the canopy of ash trees from some distance. These galls are caused by the ash flower gall mite, which is not a true insect. While unsightly, these galls pose little actual threat to the health of the tree.
Disease Problems Associated with Ash Trees
The most common source of ash canopy thinning and death in Wisconsin is a fungus disease called Verticillium. The fungus clogs the vascular system so the trees have scorched leaves and a thinning canopy. Tree symptoms look very similar to Emerald Ash Borer but there will be no S-shaped galleries under the bark and no D-shaped exit holes on the trunk.
Ash Yellows is another disease that causes trees to decline and die over time. Ash yellows is caused by a bacteria-like organism known as a Phytoplasma. It is thought that leafhoppers can carry the disease from tree to tree. Infected trees tend to have small chlorotic leaves and may display brooming at the tips of branches.
If you suspect that your ash trees are suffering from a disease, the UW-Madison Plant Disease Diagnostic Clinic can provide assistance in disease identification. Information on submission of samples to the disease clinic can be found on their website.