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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis
Larva and tunneling of the emerald ash borer
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Emerald Ash Borer

Posted by John Fulton -

There have been many findings of the emerald ash borer in central Illinois over the two years, including Bloomington, Chenoa, LaSalle County, and Bureau County. What does this mean for us? It means the borers have been active and undetected in areas for a long period of time. That is part of the problem with the emerald ash borer: it can be in a tree for three to five years before any visual symptoms are available to help us diagnose the problem.

Add into the equation there are other diseases and boring insects that cause similar problems, and we end up with some confusion. Much of the information Illinois is using has come to us from Michigan State University, where they have been battling the problem for many years. Symptoms of infestation of emerald ash borer include canopy dieback, shoots coming from the base of the tree, splitting bark, serpentine feeding galleries under the bark, increased woodpecker activity, and "D" shaped exit holes. Remember, many other problems cause many of these same symptoms.

Emerald ash borer does not do well moving from one place to another on its own. Most of the help comes from humans moving firewood, lumber, or other items made from infested trees. This movement of products is why the insect "leapfrogs" from one place to another, often many miles away.

Many people have asked to have their ash trees looked at to see if they have it. That is all well and good, but remember it can be in your tree for up to five years before it shows any symptoms that can be seen. The other question is how do I save my ash tree? To that end, here are some of the things to look at when considering an attempt at insecticidal control.

Phil Nixon, Extension Entomologist, has several things to look at in his list. First, the only certain method to control emerald ash borer is to remove the tree. This sounds extreme, but any control attempt is only effective in the 80 to 90 percent range. Second, the cost of treatment over a span of years should be looked at. It might only cost $35 to treat for one year, but that will really add up over 20 years with increasing costs each year. And third, a tree in a regulated are is subject to removal by governmental agencies regardless of whether it has been treated or shows signs of infestation.

There are treatment options for professionals and homeowners. It is recommended to preventatively treat ash trees no more than 15 miles from known infestations. Control is usually more effective on smaller trees, and treatment is not as effective on trees already infested. The major treatment option for homeowners is to apply Merit (imidacloprid) insecticide as a soil treatment on an annual basis. This treatment will be more effective in the spring, and it takes a month or two to translocate in the tree. Also remember your tree can still be cut down if it is in the zone of a known infestation, whether it has been treated or not.

If you see emerald ash borer or its damage, you may call the Extension Office at 732-8289 or the Illinois Department of Agriculture at (800)641-3934. More information is available online at and

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