Emerald Ash Borer

It has been nearly 10 years since the emerald ash borer (EAB) was first discovered killing ash (Fraxinus spp.) trees in southeastern Michigan. Knowledge gained since the discovery has been quite amazing. Whether it is an understanding of its lifecycle and biology, exploring biological controls, discovering host plant preferences and genetic diversity, or knowing insecticide options and efficacy, researchers continue to learn. And educators continue to spread the knowledge.

Shortly following the discovery in Michigan, EAB was also found in Windsor, Ontario. Additional discoveries have included: Ohio in 2003; Indiana in 2004; Illinois and Maryland in 2006; Pennsylvania and West Virginia in 2007; Wisconsin, Missouri and Virginia in summer 2008; Minnesota, New York, Kentucky in the spring of 2009; Iowa in spring of 2010; and Tennessee in the summer of 2010. Populations in the core are rapidly growing and expanding quickly. Some of the outlying infestations are relatively small, but will continue to spread. The USDA/APHIS infestation map is updated on a monthly basis, and links to the maps are available on http://ashalert.osu.edu.

If we take a closer look at Ohio, 57 of the 88 counties have reported and documented EAB infestations. While EAB is wide-spread through much of Ohio, the following counties do not have a documented find of EAB: Adams, Ashtabula, Athens, Belmont, Brown, Carroll, Columbiana, Coshocton, Crawford, Fayette, Gallia, Guernsey, Harrison, Highland, Hocking, Holmes, Jackson, Jefferson, Knox, Madison, Meigs, Monroe, Morgan, Muskingum, Noble, Preble, Ross, Stark, Tuscarawas, Vinton and Washington.

While questions about EAB are numerous, the two most common questions that extension receives include:

• Can trees be protected from EAB?
• What can be done if my trees are dying or dead?

EAB has been found in ash trees in 15 states. Insecticide treatments can be effective in protecting trees.

Insecticide treatments can be effective, protecting ash trees from EAB. More extensive information can be found in a multi-state IPM bulletin entitled “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” at http://www.ashalert.osu.edu, following the link to Factsheets/Bulletins. Below are key points to consider when exploring insecticide treatments.

• Insecticides can effectively protect ash trees from EAB.
• Unnecessary insecticide applications waste money. If EAB has not been detected within 10-15 miles, trees are at low risk. Be aware of the status of EAB in the area.
• Trees that are already infested and showing signs of canopy decline when treatments are initiated may continue to decline in the first year after treatment, and then begin to show improvement in the second year due to time lag associated with vascular healing. Trees exhibiting more than 30 percent canopy decline are unlikely to recover even if treated.
• Insecticide applications are most effective when made preventively in the spring in time to render the tree toxic before adults begin to feed on foliage and newly hatched larvae enter the tree.
• Emamectin benzoate is the only product tested to date that controls EAB for two years with a single application.
• Soil drenches and injections are most effective when made at the base of the trunk.
• Soil injections should be no more than 2-4 inches deep, to avoid placing the insecticide beneath feeder roots.
• To facilitate uptake, systemic trunk and soil insecticides should be applied when the soil is moist but not saturated or excessively dry.
• Research and experience suggest that effectiveness of insecticides has been less consistent on larger trees. Research has not been conducted on trees larger than 25-inch DBH.

When treating large trees under high pest pressure, it may be necessary to consider combining two treatment strategies.

• XytectTM soil treatments are labeled for application at a higher maximum rate than other imidacloprid formulations, and we recommend that trees larger than 15-inch DBH be treated using the highest labeled rate. Merit imidacloprid formulations will soon be labeled for use at this higher rate.
• Treatment programs must comply with label restrictions on the amount of insecticide that can be applied per acre in a given year.

Questions on utilizing infested ash trees increase as EAB moves through a region. To address this issue, a fact sheet was written and posted on www.ashalert.osu.edu.

Check out this other online resource for regional EAB information. www.emeraldashborer.info.

Reprinted with permission from the March 2012 issue of The Buckeye magazine. Courtesy of The Ohio Nursery & Landscape Association.