Amid the announcements of mass school closings and warnings of cold temperature-related maladies, Minnesota entomologists are excited about the possible effects that freezing temperatures could have on the emerald ash borer (EAB). The hope is that the extreme weather will freeze and subsequently kill the larvae of the EAB, an invasive species of insect that attacks and kills ash trees. This could be welcome news for Winona, which has a large number of ash trees of various varieties.
With temperatures this past Monday reaching -18 degrees for several hours, the possibility of decreasing the population of EAB is plausible, but the cold still may not kill all the larvae, according to Lee Frelich, director of the Center for Forest Ecology at the University of Minnesota.
“The bark of trees are pretty good insulators, and that’s where the bugs are,” Frelich explained. “It ranges usually anywhere from three to seven degrees warmer under the bark of a tree.”
“At -20 degrees, 79 percent of the EAB population would be expected to die,” Frelich said. “But this would have to last quite a while because bark is a good insulator.”
The bark acts as a barrier, so it takes longer periods of time for sub-zero temperatures to penetrate and eventually freeze the EAB larvae. Colder temperatures are also needed because the insects have natural chemicals that help prevent them from freezing.
Nevertheless, below zero temperatures for an extended period of time will kill a good portion of the EAB larvae. The freeze may not eliminate the entire EAB population, but it will help to slow the rate of spread.
“There should be a lower population,” Frelich said. “Of course, we won’t know until spring.”
Emerald ash borer
in Winona County
According to the Minnesota Department of Natural Resources (DNR), Winona is one of four Minnesota counties with a quarantine on ash wood due to an EAB infestation. “[EAB] has been found here and we’re on a quarantine of ash wood,” Jill Johnson, special projects coordinator for Winona County, explained. “We can’t move it out of the county.”
The Minnesota DNR has listed the following as signs of an EAB-infected ash tree: heavy woodpecker activity on the tree, dying branches in the top canopy, sprouts around the base of the tree, vertical cracks in the bark, S-shaped tunnels under the bark and 1/8-inch D-shaped exit holes in the bark.
To report an EAB infestation, contact the Arrest the Pest Hotline at 888-545-6684.