Emerald ash borer (EAB), a nonnative invasive beetle, has spread throughout much of the United States and Canada and has killed millions of ash trees. In urban areas, where ash trees are commonly planted, insecticides are used to protect ash trees from the insect. However, arborists have noticed that ash trees heavily infested by EAB often continue declining and die even with insecticide treatment. In research led by Charles Flower of the University of Illinois, university and Forest Service scientists at the agency’s Northern Research Station conducted a study of ash trees experiencing different initial levels of decline from EAB. The initial condition of the tree was assessed with a quick and easy rating system. Trees were treated with emamectin benzoate or left as controls, and then tracked for 3 years. During this time all of the untreated trees died while the trees that were initially healthy or initially exhibiting symptoms of canopy thinning were kept healthy by the insecticide. Trees that initially had dead branches declined or died. Arborists, homeowners, forest managers, and urban planners can use this information as they plan treatment of ash trees in EAB-infested areas so they don’t waste time and money treating trees that are already too far gone.