Treatment for emerald ash borer works best on a tree that retains half or more of its canopy, suggests Wisconsin Horticulture. Trees with less than half of their canopy remaining seldom recover, and removal is the best option.
Emerald ash borer responds best to pesticides containing imidacloprid, according to Wisconsin Horticulture. However, it is best to completely remove badly damaged trees entirely, rather than go to the expense of pesticide treatment. Homeowners should also consider contacting an arborist or a similar professional for a consultation before performing any extensive treatments.
The emerald ash borer is native to Asia, says the Illinois Department of Agriculture. It likely arrived in North America in packing materials and is now an invasive species that presents a serious threat to North American ash trees.