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It's the time of year to treat valuable ash trees against emerald ash borer

Contact(s): Bill McNee, DNR forest health specialist, Bill.Mcnee@wisconsin.gov, 920-360-0942
April 2, 2019

MADISON - State forest health specialists recommend homeowners consider insecticide treatment of healthy, valuable ash trees to protect against emerald ash borer. This pest kills more than 99 percent of the trees it infests and is currently the biggest threat to Wisconsin's ash trees.

While some EAB larvae may have been killed by cold winter weather, it is unlikely frigid temperatures were enough to delay ash tree mortality in most parts of Wisconsin, said DNR forest health specialist Bill McNee.

Signs of EAB infestation include woodpecker damage where the birds pick away bark to feed on larvae. - Photo credit: DNR
Signs of EAB infestation include woodpecker damage where the birds pick away bark to feed on larvae.Photo credit: DNR

Insecticide treatments to protect ash trees are usually applied between mid-April and mid-May, so it is important to start planning now.

The highest risk of EAB infestation is within 15 miles of known activity, but it is widely believed that additional, undetected infestations are located throughout the state. For a map of known infestations in Wisconsin, visit the Wisconsin EAB portal.

*The first thing homeowners can do is check their ash trees for signs of infestation. Woodpecker damage is easy to see this time of year and is often the earliest visible sign that EAB is present. Homeowners can read this factsheet from the University of Wisconsin-Extension to help identify EAB infestation and to decide whether a tree is worth treating.

Forest health specialists recommend developing a treatment plan now if signs or symptoms of EAB infestation are present or if EAB has been found locally.

While the best time to treat ash trees is before they are infested, treatment of already-infested trees can be successful if done while EAB populations within the tree are still low or moderate. Some ash trees may be too heavily infested to save or they may have other problems that make them poor candidates for treatment. Homeowners can consult a certified arborist to discuss whether infested trees are good candidates for treatment.

Treatments are not economically practical for ash found in woodlots. Any questions about woodlot management can be directed to a professional forester.

Additional information about emerald ash borer signs, symptoms and management can be found on the DNR website and through the Wisconsin EAB portal.

Last Revised: Tuesday, April 02, 2019

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