Minnesota's ash borer outbreak was inevitable
By John Weiss
Date Modified: 10/06/2011 10:00 AM
DAKOTA, Minn. — Eleven Winona County, state and federal officials fanned out Sept. 20 near Dakota, at the site of the state's first outbreak of emerald ash borer to try to find out how many trees the invasive beetles have killed or are killing.
They found more than 50 infected ash trees within a small area at the Winona County Road 12 interchange with Interstate 90, while at least one more was seen in nearby Great River Bluffs State Park.
Mark Abrahamson wasn't surprised.
"It was bound to happen sooner or later," said the ash borer expert with the Minnesota Department of Agriculture and leader of the survey.
Tree-killing beetles have been slowly moving westward and adult beetles have been found in traps in the Twin Cities, southeastern Houston county and recently, one each in La Crescent, the park and nearby La Moille.
This is the first time, however, that infested trees have been found, Abrahamson said. One tree is already dead and could be the grandfather of the outbreak, while others are dying or have beetles burrowing S-shaped tunnels under their bark. That slows the movement of nutrients to the top of the tree, slowly killing it.
Because nearly all were found in one small area, that may be the epicenter of Minnesota's first outbreak. There are likely more outbreaks because the beetles found in La Crescent or La Moille probably came from other infestations. No one knows how beetles got into that first tree, he said.
So far, no one has found a way to stop the beetles, though they can be slowed, he said. The department released stingless wasps in the park last week and plan to release more around the infestation this week. They are from China, where the beetles came from, and prey on the beetles' eggs or larvae.
"You don't get rid of the pest; you hope to bring it down to levels that are acceptable," said Abrahamson who first noticed the dead or dying trees a week ago.
The only good news for that area is ash trees make up fewer than 10 percent of trees, said Doug Rau, a DNR area forestry supervisor in Rochester.
That means that even if the beetles do begin widespread infections, "for most people, they are not even going to notice anything different has happened," Abrahamson said.
When it gets into urban areas, inoculation and other methods of control might be feasible, he said.
Besides the large dead or dying trees, officials also found beetle larvae or signs in much smaller trees.
"It's amazing the little ones are getting hit," said Sue Burks, DNR forestry invasive species program coordinator.
That would indicate the beetles have been here for several years, she said.