Emerald ash borer (EAB) adults are expected to begin emergence in northern Illinois within the next week. They were observed emerging in Columbus, Ohio, on May 23 by Dave Shetlar, Ohio State University entomologist. At that time, he observed one emerged adult, two current-year emergence holes, one pupa, and six adults in the process of chewing their way out of the tree. The tree was located in a park that was lightly infested with EAB. Phenology observances that he made at the time included Delaware’s black locust trees at half bloom, Miss Kim–type lilacs in full bloom to beginning to decline, and Japanese tree lilacs in full bud but no blooms yet.
Several factors should be taken into consideration before applying insecticides to control emerald ash borer. We recommend that preventive treatment of ash trees should not occur more than 15 miles from known infestations. Typically, EAB adults fly about 1/2 mile during their lifespan. In areas where the infestation is still light, which is the case in Illinois, the beetles typically do not fly very far because there are still plenty of live ash trees nearby to infest. As the infestation increases, and most of the ash trees are dying, the beetles fly farther to find new hosts. In these cases, it is thought that they may fly more than 1/2 mile per year. Even so, there is sufficient cushion built into the 15-mile recommendation to cover these variances. With systemic insecticide treatment, there has been 80 to 90% survival of trees with up to 40% dieback, so most trees can still be saved even after EAB is present.
Control of EAB is more effective on smaller trees, those with a trunk diameter of less than 10 inches. Insecticide labels include higher rates for larger trees. It typically takes 2 years for systemic insecticides to move throughout the tree; it may take longer for larger trees.
Professional insecticidal control options recommended by the University of Illinois include the following:
- Imidacloprid (Merit, Xytect) applied onto or injected into the soil around the tree annually within 2 feet of the trunk. Do not apply into mulch or other dead organic matter.
- Imidacloprid (Merit, IMA-jet, Imicide, Xytect, Pointer) injected into the tree annually.
- Emamectin benzoate (Tree-age) injected into the tree annually.
- Dinotefuran (Safari) applied in Pentrabark onto the trunk annually.
- Foliar and bark sprays of bifenthrin (Onyx), cyfluthrin (Tempo), permethrin (Astro), or carbaryl (Sevin) in both mid-May and mid-June to control visiting beetles.
There are several factors to consider with the above recommendations. Foliar and bark sprays to control visiting beetles should be used only when a new infestation is located during beetle-flight season. Soil or trunk injections are the preferred method of control. Observe labeled acre rates of insecticide application. Although several states have increased the amount of imidacloprid that can be applied per acre to account for parks and other sites where trees are numerous, the rates have not been increased for Illinois. Where there are many trees per acre, you may need to use more than one insecticide to stay within labeled acre rates.
Soil injections typically take 1 to 2 months to move throughout the tree. Trunk injections are much quicker, taking about 2 weeks to move throughout the tree although it takes 2 years to fully protect the tree. Applications can be made at any time of the year, but they are most effective in the spring. With both soil and trunk injections, transpiration appears to be the driving force in moving the insecticide through the tree. The leaves create much of this transpiration, and they are most active during the first half of the growing season. Although fall application has shown good results, insecticides start breakdown after application. Having several months pass before the insecticide moves effectively through the tree results in reduced efficacy.
Early research indicates that emamectin benzoate provides almost 100% control of EAB larvae for 2 years. Imidacloprid and dinotefuran provide around 90% control for over 1 year. There has been a lot of excitement about emamectin benzoate based on this research, but realize that the other systemics provide a very high level of control as well. It appears that ash trees can tolerate up to 30% infestation of EAB without dieback, so all of the systemics should be effective. Until more research is conducted, we are recommending annual treatments, even with emamectin benzoate.
Realize that soil injections do not injure the tree, as occurs with trunk injections. There is also considerable variability in the size of the holes used with various trunk-injection methods. Arbor-jet is the only company with an emamectin benzoate label, and its imidacloprid application shows the highest control. However, its injection method also creates the largest hole of those recommended. The amount of trunk damage is likely to be less with other injection options that create smaller holes in the trunk. An updated fact sheet containing these and homeowner recommendations, as well as other control information for EAB, can be found at http://www.ipm.uiuc.edu/.