Emerald Ash Borer treatment
Hello! For the past 6 years, I have been having the ash trees on my residential property professionally treated every other year for prevention of emerald ash borer. The treatments have been successful, with the trees showing no sign of infestation. Ash trees on neighboring properties are mostly dead or dying, but have yet to be removed. Due to cost, I am considering extending the interval between treatments to 3 years, but not at the expense of losing the trees that I have already invested to save. Is there scientific research to support this approach? If I defer treatment, can I watch the trees closely for early signs of infestation, and treat during summer if necessary? Thank you.
Midland County Michigan
The latest research is showing some insecticides are effective for 3 years. So, it depends on what is being used, dosage, and how it is applied. Emamectin benzoate injections, ( one brand is Tree-age) can protect for three years. Soil drenches or basal sprays protect for one or two years. This document updated in 2019 explains the treatment options available and how long they are effective:
Two years after all untreated trees in your area are dead, your treated trees may be able to go to a 4-5 year cycle because the borer insect population will be very low. This response to another client in a location where all untreated trees were dead explains:
“Here is a synopsis of recommendations by Drs. David Smitley, MSU Landscape Entomologist, and Deb McCullough, MSU Forest Entomologist. Both researchers have worked extensively on EAB since it was discovered in Michigan.
Since we’re at the point where most of the untreated ash trees in Midland are dead, you can extend the treatments to a 4 or 5-year treatment plan. Here are the strategies to consider:
1. Emamectin benzoate trunk injection at the highest label rate once every five years. If you see new bark splits and limb dieback in the future, treat a year or two early, then go back to the 5-year schedule.
2. If the tree is under 14 inches DBH (trunk diameter in inches at breast height), apply emamectin benzoate at a moderate rate, e.g, 5 ml per diameter at DBH inch. (This option is a consideration since the high rate can be difficult to get into trees. Plus, the treatment doesn’t cost as much.) Trees should be treated at either 4 or 5-year intervals. For trees with a DBH over 14-16 inches, then the high rate might be better.
Note that if you follow a 4 or 5-year treatment plan, it would be wise for someone to examine a few green ash trees in August. Those are likely to be colonized before any white ash trees. If new woodpecks, declining branches or any other new signs of EAB are observed in green ash, then the EAB density might be starting to build at least a bit. At that point, it might be worth shortening the injection frequency – e.g., switching from 5 to 4 years, for example. —-Mary Wilson, MSU Extension, Horticulture Educator”
From your description you should be able to go to a 3 year cycle when using Emamectin benzoate injections at the correct dosage. Once all untreated trees are dead, a longer treatment cycle can be used. Thank you for using our service.