Treat your ornamental ash trees for emerald ash borer this spring

A yellow ornamental ash tree at peak fall color. This tree is worth treating to protect it from being killed by emerald ash borer.

High-value ash tree at peak fall color.

March is a good month to consider insecticide treatments for high-value ornamental ash trees this spring. Emerald ash borer (EAB) has been found in 42 Wisconsin counties and is expected to be more than 99% fatal to ash trees that are not protected with insecticide every 1-2 years. Many insecticides used in EAB treatments are applied between mid-April and mid-May, and now is a good time to contact a tree service or other pesticide application business if arranging for professional insecticide treatments.

Property owners with susceptible ash trees should consider a number of factors when deciding to treat their ash trees, including financial cost, tree condition and location, the shade a tree provides, its contribution to property values, and aesthetic view. Homeowners should also consider the financial cost of removing a tree that is killed by EAB, and the benefits that a dead tree no longer provides.

The ash trees in much of Wisconsin are at high risk for becoming infested soon if they are not already infested. Ash trees within 15 miles of a known infestation are at highest risk of EAB infestation, even if they are not yet showing symptoms of being infested. Mountain ash is NOT susceptible to EAB, and does not need to be protected from this insect.

If a tree is lightly or moderately infested, properly-done treatments should provide good protection even as adjacent, untreated trees become infested and die. Some of the insecticide products can be purchased and applied by property owners, whereas other products are only available to tree care professionals. The treatments are not practical for low-value, woodlot ash trees and forest landowners are encouraged to contact a forester about managing EAB on their property. 

Follow product label instructions so that insecticides are safely applied and properly timed for optimal effectiveness. More information about emerald ash borer infestations and insecticide treatments can be found online.

Written by: Bill McNee, forest health specialist, Plymouth (, 920-360-0942.

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