Insecticide treatments only are effective in holding off the emerald ash borer if they are applied before an infestation is serious, research shows. By the time symptoms are obvious, borers may have been at work on a tree for months or years and it may be too late to stop them. So if you decide to try and save a tree, Arboretum experts say, it is important not to wait to begin treatments until you see major damage. Treating while an ash tree still seems healthy may forestall an infestation.
Treating against EAB is a long-term commitment, since most treatments need to be reapplied annually. Certified arborists can confirm that a tree is infested or apply treatments, although there also are versions of some insecticides that can be applied by homeowners.
It’s also important to keep the tree healthy, by fertilizing in the fall or spring and watering when conditions are dry. Trees should receive the equivalent of 1 inch of rain during the growing season. Research suggests that insecticide treatments may be more effective against the emerald ash borer if the tree is healthy overall.
There is one way all of us can help defend ash trees: Do not move firewood! Researchers believe that the EAB spread from Detroit throughout the Midwest since 2002 mainly by hitching rides in firewood, perhaps when it was carried between vacation homes or campsites and homes. If you go away for the weekend, buy firewood when you get there and do not bring any home. If you order firewood locally, ask where it came from and be sure it was cut nearby.
Learn more at the Plant Advice page of the Arboretum's website.