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Anti-freeze: Ash borers expected to survive winter, keep on killing trees

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Frank Schultz
February 28, 2014

Abandon all hope, ye who thought this cold winter would kill off the emerald ash borer.

The counties along the Illinois border, from Rock County and eastward, are rife with the tree-killers, and everyone should plan accordingly, a Wisconsin Department of Natural Resources forester said.

Homeowners who want to save the prized ash trees in their yards should be planning to treat them with insecticide this spring, said Bill McNee, forest health specialist.

Most of the ash borer larvae now living under the bark will survive the cold, he said.

“There will be some mortality, but you would not expect that it's going to make a difference in the emerald ash borer population growth and the decline of the trees,” McNee said Friday.

McNee said the emerald ash borers come from an area of east Asia that is at least as cold as it is here. The scientific consensus is that the extreme cold might kill a few of the larvae as they winter under the bark of ash trees, but it won't slow their spread much.

They are so well adapted, in fact, that their bodies manufacture anti-freeze, McNee said.

With each adult female laying 50 to 100 eggs this spring and summer, the emerald ash borer population should be booming, now that it has gained the local foothold, McNee said.

McNee recently confirmed two new infestations in Walworth County, one in a marshy area next to Pell Lake and one in the town of Delavan just north of Williams Bay on the west end of Geneva Lake.

Those sites are more evidence the southern halves of Walworth and Rock counties are full of the killer beetles, as part of a wider infestation in northern Illinois, McNee said.

McNee expects a rapid decline in ash trees as the emerald ash borer population builds in these area.

Without treatment, ash trees will fade and die, McNee said. “It's a matter of not if, but when.”

Trees are typically treated in April and May, so the insecticide is already in the tree when they're attacked in late spring and summer, McNee said.



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