Preventing Defoliation by Spongy Moth ( Lymantria dispar ) with Systemic Insecticides and Their Interaction with Nitrogen Supplementation

Background Spongy moth ( Lymantria dispar L.) is an exotic, outbreak pest in North America, where it causes defoliation and mortality of trees. The management tools for this insect on residential and commercial properties as well as small woodlots include the use of systemic insecticides to protect against severe defoliation during an outbreak. Methods We evaluate the ability of acetamiprid (TriStar ® 8.5 SL; Nufarm, Alsip, IL, USA) applied as a bark spray in the spring; acephate applied as either a soil injection (Lepitect ™ ; Rainbow Ecoscience, Minnetonka, MN, USA) or root flare injection (Lepitect Infusible ™ ; Rainbow Ecoscience) in the spring; and emamectin benzoate (Mectinite ® ; Rainbow Ecoscience) applied as a root flare injection either in the previous fall or spring to prevent defoliation of mature northern red ( Quercus rubra ) and white ( Q. alba ) oaks during a spongy moth outbreak. We also evaluated any potential influences of nitrogen (N) supplementation on the efficacy of acetamiprid and fall emamectin benzoate treatments to prevent defoliation by spongy moth. Results No effect of N supplementation on foliar N levels or insecticide efficacy was detected. All insecticide treatments, except for bark-applied acetamiprid, were able to significantly reduce spongy moth defoliation relative to nontreated controls, though there were statistical and numerical differences between treatments. Conclusions These results demonstrate that N supplementation requires further study but did not influence insecticide efficacy in our study and that acephate and emamectin benzoate are both effective at preventing defoliation, but due to variation between treatments, considerations should be made regarding the timing and method of application.