Winter cold had little chilling effect on emerald ash borer spread

Winter cold had little chilling effect on emerald ash borer spread

To hear more on how the emerald ash borer was affected by persistent cold last winter, click here.

AMES, Iowa – Record-cold temperatures this past winter were a death knell for some insect populations, and for others, hardly meaningful.

Statewide temperatures from December through February averaged 14.6 degrees Fahrenheit, fully 7.5 degrees below normal. That’s great news in terms of controlling early season bean-leaf beetles, which struggle to survive below the 14-degree mark.

But there’s another pest cutting a swath across the state: the emerald ash borer. The half-inch-long bug is a multi-billion-dollar problem for the state, but as Iowa State University Forestry Professor Janette Thompson points out, the weather probably won’t have had much affect on its population.

“So, it’s really pretty much with this bug not weather-related; it’s whether it’s here, or it’s not,” explains Thompson. “And the most sure way of detecting the insect is actually to peel up the bark. So, in the winter there’s not a lot between you and the tree, right? There’s no foliage; you can get a pretty good view of the tree; you know which trees to look at, and then just peeling up the bark reveals those galleries.”

The discovery of the emerald ash borer in Jasper county in central Iowa late last month raised the tally of infested Iowa counties to 9. The whole state is currently under a quarantine to slow the insect’s spread, but given that the adult emerald ash borer can only fly 5 miles, Thompson says it’s no mystery how the insect has shown up in counties up to 300 miles apart, such as Union County and Allamakee County.

“Humans have been the biggest vector of this pest,” says Thompson. “The initial dots on the map really followed interstate highways, and it was firewood. It was people from Detroit who go upstate for their vacation, with firewood from dead trees.”