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Posted 8 June 2009. PMN Crop News.

Treat or Not Treat Ash Trees for Emerald Ash Borer? New University Bulletin Provides Guidelines, Trial Results

Ohio State University.

Wooster, Ohio (May 28, 2009)--Homeowners, arborists and tree-care professionals can now access unbiased, science-based information to determine whether or not to treat ash trees for emerald ash borer (EAB), which insecticide may be better suited for a particular tree, and when and how treatments should be made for best results.


The new guidelines and a summary of trial results are included in “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer,” a bulletin co-authored by entomologists with Ohio State University, Michigan State University, Purdue University, University of Wisconsin-Madison, and University of Illinois at Urbana-Champaign.

The bulletin is available online at (click on “Fact Sheets/Bulletins”). If you don’t have Internet access, contact your local OSU Extension office for assistance.

An invasive insect first found in North America in 2002, EAB has destroyed millions of ash trees in Ohio and neighboring states. So far, the voracious beetle — which only attacks true ash trees in the Fraxinus genus — has been confirmed in 12 Midwestern and eastern U.S. states and in two Canadian provinces.

“Our understanding of how EAB can be managed successfully with insecticides has increased substantially in recent years,” said lead author Dan Herms, an entomologist with the Ohio Agricultural Research and Development Center (OARDC) and OSU Extension. “There are effective treatments available for both professionals and do-it-yourselfers, including some that are applied in the soil, injected in the trunk of the tree, or sprayed on the trunk, branches or foliage.”

But before rushing to the garden center or contracting a professional applicator, Herms said, homeowners should first consider their proximity to EAB infestations, how much damage EAB has done to their trees, their budget and how much they value their ash trees.

Location is important for determining whether and when to begin treating. If your property is within a county that has been quarantined for EAB, your ash trees are probably at risk of becoming infested. Similarly, if your trees are outside a quarantined county but within 10-15 miles of a known EAB infestation, they may also be at risk. However, if your trees are more than 15 miles from the nearest infestation, it is probably too early to begin insecticide treatments.

So far, half of Ohio’s 88 counties have been quarantined because of EAB. For the latest information on quarantines and maps, go to or call (888) OHIO-EAB. If your ash tree is already infested and has lost more than 50 percent of its canopy, Herms said, it is probably too late to try to save it. Even when treatment is started early in the infestation, signs of improvement may not show until the second year of treatment as the tree needs time to repair its vascular system.

Budget, of course, is another important consideration. Most available insecticides need to be applied every year to be effective, which can be expensive. However, there’s a new product (emamectin benzoate, only available through professional applicators) that is effective for two years or even longer.

“These treatments are not cheap, and it may be more cost-effective to replace the ash trees with other species,” Herms pointed out. “But some people have a strong emotional attachment to their trees, and for them it may be worth investing in these insecticide treatments. Landscape trees also have other benefits, such as increasing property value, providing shade and cooling, and increasing the quality of life in a neighborhood. So there are many factors to take into account when making this decision.”

University-tested insecticides include imidacloprid, which can be applied by soil injection, soil drench or trunk injection. Imidacloprid is available in a variety of formulations and under several trade names. Depending on the formulation and application method, it can be applied from mid- to late spring, from early May to mid-June, or in the fall.

While most imidacloprid products tested are intended only for professional use, one formulation — Bayer Advanced Tree & Shrub Insect Control — is available for use by homeowners as a soil drench. Several generic products containing imidacloprid can also be purchased at garden stores, but their formulations vary and their effectiveness has not been evaluated in university tests, Herms said.

The rest of the products included in the bulletin are intended only for professional use. They are emamectin benzoate (trunk injection, early May to mid-June); Bidrin (trunk injection, early May to mid-June); dinotefuran (systemic bark spray, early May to mid-June); and several preventive bark and foliage cover sprays (permethrin, bifenthrin, cyfluthrin and carbaryl).

OARDC and OSU Extension are the research and outreach arms of Ohio State’s College of Food, Agricultural, and Environmental Sciences.

Dan Herms,
Entomology, OARDC and OSU Extension