Protecting ash trees from emerald ash borer

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

After three years of testing at several different locations we now know that imidacloprid applied as a basal soil injection (by arborists) or as a basal soil drench (by homeowners) works well to protect healthy trees from emerald ash borer. The key is to start early before seeing any signs of canopy thinning or dieback due to emerald ash borer. If you are in an infested area and some trees in the area are already showing signs of infestation the safest option is to do a basal soil drench and a trunk injection the first year.

Homeowners can do the basal soil drench themselves. They can purchase Bayer Tree and Shrub Insect Control (containing imidacloprid) at a local garden center. It comes in a 32 oz blue plastic bottle. Pour one ounce of this product for each inch of circumference around your ash tree into a bucket, fill the bucket with water, and pour the solution around the base of the trunk sometime between now and June 1. The basal drench needs to be repeated each spring to provide reliable protection. It takes two years of treatments on larger trees (>6” dbh) to provide adequate protection. The cost for treating a 10” dbh trees is approximately $25 per year.

ACECAP implants containing acephate is another systemic insecticide product that can be used by homeowners in May. In our test results the ACECAP implants did not work as well as the imidacloprid basal drench in the second year, so I suggest only using the basal drench for healthy trees, or perhaps a combination of both the basal drench and the ACECAP implants the first year, then only the basal drench in subsequent years.

If homeowners prefer to hire an arborist, now is the time to contact one. Most of the treatments are done in the spring. The advantage of hiring an arborist is that you will get their expert opinion on when to begin treatments, if it is too late or not, and how to water and fertilize ash trees which will help treated trees survive borer attack.

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