DNR encourages property owners to protect ash trees against emerald ash borer

MADISON, Wis. (WSAW) - The Wisconsin DNR wants property owners with healthy, valuable ash trees to treat them with insecticide this spring to protect against the deadly emerald ash borer.

The pest is the most damaging threat to Wisconsin trees, killing more than 99% of the untreated ash trees it infests.

A common, early sign of emerald ash borer infestation is woodpecker damage that is created when birds feed on emerald ash borer larvae beneath the bark of ash trees. Treatment of infested ash trees is more likely to succeed if the trees have low or moderate levels of woodpecker damage. Treatments are typically done between mid-April and mid-May.

Treatments are applied every year or two depending on the product. Homeowners can apply some insecticide products, and others must be applied by a certified professional. Review the available options before selecting an insecticide and treatment method.

Some ash trees are not worth treating due to pre-existing health or structure problems, so removal and replacement can be better options. You can search for a certified arborist on the Wisconsin Arborist Association website and International Society of Arboriculture website.

In 2022, emerald ash borer was found in five additional northern counties and is now known to be present in 66 of Wisconsin’s 72 counties. The insect is likely present in other locations but has not been detected. The highest risk of infestation is in communities already known to be infested or within 15 miles of a known infestation.

Stay informed and be on the lookout for emerald ash borer. Know where the pest has already been found and look for the signs and symptoms of emerald ash borer infestation. Watch ash trees for the following:

Woodpecker damage called “flecking,” where pieces of bark have been removed while feeding on emerald ash borer larvae beneath the bark. It usually starts up in the canopy and progresses down the tree over the next few years if the tree is not treated.
Sprouts growing from the base or trunk of the tree.
Thinning canopy with smaller, pale leaves.
Small, one-eighth-inch, D-shaped exit holes in the bark.
Green beetles crawling on the trunk of ash trees during the summer.

For more information on the impact of the emerald ash borer, click here.