Emerald Ash Borer confirmed in Waukesha County

Emerald Ash Borer confirmed in Waukesha County
Kristin Krokowski, Commercial Horticulture Educator, UW-Extension Waukesha County

Emerald Ash Borer, a serious pest of ash trees has been confirmed in the Mukwonago area of Waukesha County. What should home owners do?

First determine if you have an ash tree in your yard. There are many websites you can visit to help you identify if any of the trees in your yard are ash trees including the Wisconsin Emerald Ash Borer website (http://datcpservices.wisconsin.gov/eab/index.jsp). You can also call the Waukesha County UW-Extension Horticulture Helpline at 262-548-7779. This pest only attacks true ash trees and cultivars in the Fraxinus family including green, white and back ash. Mountain Ash and Prickly Ash trees are not affected.

If you have an ash tree in your yard that you wish to protect from the Emerald Ash Borer there are several options available. Homeowners may treat their own trees using a soil drench. A soil drench is taken up by the roots of the tree and moved throughout the trees vascular system. Insecticide treatments for homeowners with the active ingredient imidacloprid are available from local garden centers. These insecticides are sold under a variety of names. Look for the active ingredient box on the label to be sure it is the right product.

It is important to apply all pesticides properly, according to the label directions to get maximum protection for your tree. Imidacloprid can be applied once a year, in the spring or in the fall. It is important that the soil not be too moist or too dry when you are applying the insecticide. Either of these conditions will prevent the insecticide from being taken up by the trees feeder roots and moving throughout the tree. If the soil is too wet, allow the soil to dry out or if it is too dry water the soil around the tree prior to applying a soil drench.

Professional arborists and landscape companies have additional options for protecting ash trees from the Emerald Ash Borer including bark sprays and trunk injected insecticides. Emamectin benzoate can be applied and protect trees up to two years. Research and experience suggest that effectiveness of insecticides has been less consistent on larger trees. Homeowners wishing to protect trees larger than 15-inch DBH should consider having their trees professionally treated. When treating very large trees under high pest pressure, it may be necessary to consider combining two treatment strategies. Keep in mind, however, that controlling insects that feed under the bark with insecticides has always been difficult. This is especially true with EAB because our native North American ash trees have little natural resistance to this pest.

If a tree has lost more than 50 percent of its canopy, it is probably too late to save the tree. University studies have shown that it is best to begin using insecticides while ash trees are still relatively healthy. This is because most of the insecticides used for Emerald Ash Borer control act systemically — the insecticide must be transported within the tree. In other words, a tree must be healthy enough to carry a systemic insecticide for it to be effective.

If you have any questions about the Emerald Ash Borer, identifying your ash tree or any other yard or garden question, please call the UW-Extension Horticulture Helpline at 262-548-7779 or email at uwex1@waukeshacounty.gov.