Frerichs Tree Service is using the recommendations outlined in Insecticide Options for Protecting Ash Trees from Emerald Ash Borer for treatment of ash trees, which is a document written for the layman by university entomologists in the Great Lakes region, where EAB made its first appearance in North America. An enthusiasm for using dinotefuran insecticide in the early stages of the threat is inspired from the research of Dan Herms during is tenure with Ohio State University. The “Insecticide Options” document, authored in part by Herms, discusses all known methods of EAB control. Effective results are indicated with three methods of treatment, and I am using these methods as itemized below. While the volume of academic studies to date is insufficient to reduce the research to a tidy numerical comparison of the efficacy of dinotefuran treatments to emamectin benzoate injection which, as of today is the obvious choice for long term treatment in high pressure EAB environments, I feel it is an appropriate interpretation of the “Insecticide Options” document to suggest that my stage 2 method described below is about 5x more powerful than the stage 1 method, and that the stage 3 method is about 5x more powerful than the stage 2 method. Also this “stretch” is made to help homeowners understand that the difference in “strength” of these products/methods is noteworthy.
IMPORTANT NOTE: THE CITY OF LINCOLN PROHIBITS INSECTICIDE TREATMENT OF ASH TREES ON CITY PROPERTY BY HOMEOWNERS. Only arborists licensed by the city can treat ash tree in right of way spaces, i.e. trees between the curb and sidewalk. At this time the only method of treatment permitted for “adopted trees” is with emamectin benzoate applied via trunk injection (described by me as “stage 3” below). It is only a matter of time before all other public ash trees will be removed by the city or it’s contractor(s). For more information about adopting ash trees click here.
Stage 1) Imidicloprid basal drench: I started phasing out use of this initial stage treatment method starting in 2017. This is the method of control available to homeowners as Bayer Systemic Insecticide sold at nursuries and box stores. Imidicloprid is a neonicotinoid insecticide commonly found in grub killers for lawn use and flea and tick collars for pets. I have found that pesticides marketed to homeowners in the retail setting are typically 7x more expensive than when purchased in bulk to professionals. For this reason I am able to provide application service for small and medium sized ash trees with the professional use equivalent product for the same cost as buying the chemical and applying it yourself. Because as of 2019 the threat of EAB in Lincoln has heightened (EAB has been detected inside city limits), and because customers of a licensed arborist will expect the highest possible rates of success in protecting their tree, this product will be in limited use for special situations going forward. Research has shown that while systemic use of imidicloprid does kill EAB larvae, it does not circulate at a rate sufficient to protect ash trees from long term loss to EAB. Neonicotinoid insecticides have been a subject of due and undue scorn in US and global headlines for a number of years. Click here for my discussion regarding the dangers of neonicotinoid insecticides.
Stage 2) Dinotefuran basal soil injection and trunk spray: While dinotefuran products labelled for use to control EAB are not marketed to homeowners, they can be purchased and used legally by homeowners on a not-for-hire basis (but not on city right of way trees). The stage 2 method has been demonstrated to be adequate to protect ash trees from low, medium, and high pest pressure with a 50-90% lethality to populations of the larvae of the insect within the tree, again reading between the lines of the research a bit. Of course, even 90% really is not good enough over the long run—ash tree owners can be expected to desire that the success of treatment be much closer to 100%. When we approach a 95% efficacy, we can compare our chance of success in long term treatment with the likelihood of your tree surviving anything else mother nature has in store for it in the way of wind and ice storms. Dinotefuran provides an adequate level of control as we anticipate significant outbreaks of EAB in Lincoln. Deciding when to move to stage three control of EAB is a wait and see process.
Stage 3) Emamectin Benzoate trunk injection. This is currently the gold standard in treatment of ash trees from EAB. Emamectin benzoate is marketed professionally in formulations that are for restricted use (licensed pesticide applicators only) and water based non-restricted use formulations of equal strength that can be legally sold to the public and used noncommercially without a license. Application equipment varies in cost from several hundred to several thousand dollars and is marketed by the same companies that sell this chemical: Arborjet of Woburn, MA and Rainbow Treecare Scientific Advancements of Minneapolis, MN. As per label instructions, this chemical protects your tree from EAB for 2 years. This is good since it means that the tree has two years to heal from injection wounds before treating again. University testing of ash trees of 18″ diameter or less has found that 100% control of EAB is achieved for 4 years after injecting at the maximum allowed/labeled rate. Trees under 25 inches in diameter injected at high rate may be treated with dinotefuran in the 3rd and 4rth years to extend the interval between drilling/injecting your tree. One study demonstrates that ash trees heal extremely well from the injection wounds, however the duration of the study is under 10 years. At the moment there is reason to be wary of a plan to drill holes in your ash tree now and to repeat the process every other year for 15-20 years while it endures attack by a vicious boring insect.
In the past it was my plan was to avoid the necessary injury that drilling (in connection with injection) causes until the EAB pressure is higher. This helps maintain a pristine vascular tissue at the prime basal injection sites when the maximum strength control method is most needed. While university level research of wound response to the injections is highly favorable, it does not make sense to disturb the best uptake sites (the root flares of your tree) before EAB has been discovered in the live tissue of more than a single tree in the Lincoln area. A potential long term disturbance (by drilling) of the precious basal root flare spaces which distribute the chemical most thoroughly throughout the tree are thus saved for years when the pest pressure is greatest. As of Spring 2022, only smaller ash trees can be treated with non-injection techniques–the bug is now too prevalent to rely on the lesser (#2 above) method.
In closing, it is worth noting that treatment chemicals and methods are changing over time. I believe it is more likely than not that methods of EAB managment, while already reliable, will continue to improve, although frankly at the moment there are no big changes on the horizon.
FINAL NOTE: The information on this site is for informational purposes only. Insecticides used to control EAB are highly toxic and more concentrated than those used in common landscape use. If you use the information on this site as guidance in treating trees, you do so AT YOUR OWN RISK. Also, it is illegal for a homeowner to treat an ash tree on city property (trees between the street and sidewalk) and there is nothing to gain in doing so since without a permit from the city your tree is slated for ultimate removal. The positioning of right of way ash trees near the street suggests that insecticides illegally applied to the soil have a very short path to contaminating Lincoln’s storm water system.