Jeffrey Hahn, Asst. Extension Entomologist
With the discovery of emerald ash borer (EAB) in St. Paul in May, many people have been asking for information on how to protect their ash with insecticides. While there are several options available to home residents within 15 miles of the infestation, the question people should be asking now is when should I treat my ash. In general insecticide applications should be made from early May until early to mid-June. With that in mind, it is really getting late to be treating your ash any longer this summer.
Photo 1: EAB galleries in infested tree in St. Paul. Jeff Hahn
It is possible that Tree-age (emamectin benzoate), which is a professional use only product, can be applied into July because its mode of action targets the larvae and not the adults. However imidacloprid relies on being taken up by the tree into the canopy and killing adults that feed on leaves. Because it takes three to four weeks for imidacloprid to be translocated in trees, any applications that take place now, will have little impact in protecting ash. This is particularly true for products available to the general public. If you are thinking of treating your ash yourself now, don’t do it. You will be just wasting insecticides. The next window of opportunity for insecticide applications will be this fall or next spring.
There are many factors to consider if you are thinking about treating your ash for EAB. For more information on insecticide options for protecting ash from emerald ash borers, please see the EAB Insecticide Fact Sheet (pdf).