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Emerald Ash Borer: Homeowner options for control and prevention

Emerald Ash Borer, a serious pest of ash trees, has been confirmed in Walworth County and several other counties of Southeast Wisconsin. Homeowners can take steps to provide their trees with a measure of security, but it must be done proactively.  From determining if you have an ash tree, to advising on what to replace one with, the UW-Extension and Master Gardener Volunteers in both Rock and Walworth Counties are here to help. Now the question is 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 (www.emeraldashborer.wi.gov).  This pest only attacks true ash trees and cultivars in the Fraxinus family including green, white and black ash.  Mountain Ash and Prickly Ash trees are not affected.

Due to the expense of yearly insecticide treatments, consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments. In addition, consider the health of each tree before treating.  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.

Imidacloprid can be applied once a year, in the spring or in the fall.  Spring applications can be applied mid-April through mid-May to Ash trees.  Although we are a bit late in the timing of imidacloprid, it would be advantageous to make an application to treat now if you live in or near Walworth County. 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. If the soil is too dry water the soil around the tree prior to applying a soil drench. No matter which insecticide you use, always read and follow the label instructions before using the product that you select. Be sure to avoid skin contact with insecticides and store insecticides where children cannot reach them. Apply all pesticides according to the label directions to get maximum protection for your tree.

Professional certified arborists, landscape companies, and certified pesticide applicators may have additional options for protecting ash trees from the Emerald Ash Borer including bark sprays and trunk injected insecticides.  For a complete list of the products available, visit www.emeraldashborer.info. See www.waa-isa.org for a list of certified arborists in Wisconsin. Research and experience suggest that effectiveness of insecticides has been less consistent on larger trees. Homeowners wishing to protect trees with larger than 15-inch diameter at chest height 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. The University of Wisconsin does not endorse commercially available insecticide products over those available directly to homeowners.

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 to receive a fact sheet with this information please call your UW-Extension office.  In Rock County call (608)757-5696 or email mike.maddox@ces.uwex.edu.  In Walworth County call (262)741-4951 or email christine.wen@ces.uwex.edu.  You can also visit www.emeraldashborer.wi.gov

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