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Ash borer a threat to millions of acres

From Jamie Robertson

Regional Cultural Center

New York Mills

Val Cervenka, forest entomologist from the Minnesota Department of Natural Resources, presented information to a small group of community members at the Bob Sonnenberg Farm on Saturday, Feb. 13 as part of the New York Mills Cultural Center's annual Talvijuhla or winter celebration.

Cervenka's presentation focused on the new (discovered in 2009 in Minnesota) exotic pest insect called the emerald ash borer. The talk was co-sponsored by the Cultural Center and the Minnesota Forest Resources Partnership. Bob Sonnenberg is past chair and current member of the Partnership and a member of the Cultural Center.

Cervenka gave a history of the insect's arrival in the Midwest-most likely, she noted, it was brought from China in infested wooden packing crates. One likely beginning point for the infestation is Detroit, Michigan. Because the native home of this insect is cold, our cold winters do not deter the beetle. And the millions of acres of ash forest in the northern Midwest are a perfect new home for the borer who has no native predators here.

From the packing crates, the insect migrated to nearby stands of ash trees in Detroit. Its rapid expansion to the forests of northern Michigan occurred from the transportation of infected wood used for firewood.

On its own, the pest can only migrate a few miles each year, but carried in firewood, Cervenka noted, it can travel the highway speed limit. It has already killed many millions of ash trees in Michigan, and the emerald ash borer was discovered in 2009 in parts of Minneapolis, though it may have been there since as early as 2002.

The insect's adult form is a metallic green beetle, and though the adults feed on ash foliage, they cause little damage. The real culprit is the creamy white larvae which bore under the bark and make tunnels or chambers as they feed. These chambers eventually cut off the flow of food to the tree, and the tree dies.

The two clearest manifestations that a tree is sick is that the top one-third of a tree begins to wilt and die and sprouts begin to grow from the base of the tree.

Cervenka noted that our millions of ash trees in northern Minnesota (there are over 800 million ash trees in the state) will be affected by the pest; the big question is how soon this will happen. At this time, safe management of firewood is the best way of controlling the rapid spread of the pest.

There are chemical treatments that can help homeowners save individual specimen trees, but those treatments are expensive, costing as much as $400 per tree. These treatments are not realistic for the vast number of ash trees in the state. Longer term, there are some experimental efforts to see if a natural predator of the borer, a wasp from east Asia, could provide some level of biological control of the pest.

To report a suspected infestation or to get information, contact the Minnesota Department of Agriculture at 1-888-545-6684.