D3148: Injecting a subset of trees confers wider protection against increasing populations of emerald ash borer

Emerald ash borer (EAB), Agrilus plannipenis, is a wood-boring insect that was accidentally introduced to North America from Asia in the 1990s. Larvae of emerald ash borer feed within the stems of mature ash trees (Fraxinus spp.), killing them. Since its arrival in North America, the insect has spread to five Canadian provinces and 35 American states. The main control strategy in urban environments is the use of systemic insecticide treatments, which can be costly when treating large numbers of trees. This five-year study investigates whether associational protection can be conferred to untreated trees by treating a subset of a susceptible urban ash population. In 2017, approximately 100 trees were selected in each of 12 sites in Minnesota with known EAB infestation. We treated a subset of trees with emamectin benzoate in 8 sites and treated a subset of trees in the remaining 4 sites with azadirachtin. We have been monitoring tree crown health to determine whether associational protection is occurring at the sites and treating trees according to each insecticide’s recommended regime. The main objective of this study is to develop a more cost effective and environmentally favourable treatment regime in urban centers.