There are an estimated 747 million ash trees in Wisconsin forests and 867 million in Minnesota forests, with millions more in cities across both states. But the Northland has the highest concentration of ash forests of anywhere in the U.S. and stands to lose vast acres of trees when the emerald ash borer takes hold here. Because it takes three or four years from their arrival until trees begin to die, the insect may already be here.
In Duluth, up to 30 percent of the city's boulevard trees are ash, city forester Kelly Fleissner said. That's more than double the species' percentage in Minneapolis, where about 140,000 trees comprising
14 percent of all boulevard trees make it the most common tree in that city.
Many of the urban ash, all of which are now threatened, were planted after cities lost tens of thousands of elm trees to Dutch elm disease over the past 40 years.
How did the bug get here?
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Native to China and Korea, the emerald ash borer apparently came to North America by hitchhiking in wooden packing crates shipped to the Detroit area in the late 1990s.
By 2002 scientists had recognized what happened, but the bugs had spread across eastern Michigan. They also have been found in Indiana, Ohio, Pennsylvania, Maryland, Illinois, West Virginia, Virginia, Missouri, the Canadian provinces of Quebec and Ontario and now Wisconsin and Minnesota.
How does it kill trees?
The adult female deposits eggs on the bark of ash trees. The larvae chew their way through the bark and into the soft layer of wood beneath, eating their way through the tree's vascular system. That cuts off the tree's flow of water and nutrients, leading to its death.
An infested tree typically loses its top leaves and sprout branches at its base in a vain attempt to save its life.
How do the bugs spread?
While the adult beetles can fly a few miles, nearly all of the major movement of emerald ash borer is the fault of humans, mostly from the transport of infected nursery trees
and firewood.
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State and federal agencies have imposed restrictions on the movement of live trees and have banned the movement of firewood into state and national parks and forests.
Emerald ash borers have no natural enemies in North America. Insecticides will kill them, but it's often too late, with trees dying before the problem is noticed.
Unlike other pests, emerald ash borers have killed 100 percent of the trees they have been found in, including previously healthy trees.
Scientists have been working to find a biological pest that will kill the emerald ash borer without causing other ecological problems, including testing a parasitic wasp from China. So far, no cure has been found. The most important preventive act: Don't move firewood. For home, cabin or campsite fires, buy or cut firewood for use only in the immediate area.
Suspect an emerald ash borer? Report any suspicious problems, especially D-shaped holes in ash trees or burrows under the bark in ash logs.
