Emerald Ash Borer could be next urban tree scourge


If and when the emerald ash borer hits the Twin Cities, “we’re never going to be talking about Dutch elm disease again,” said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board.

The species-specific bug has no preference for the kind of ash tree it infests, liking them all: green, black and white ash. In Minneapolis, where ash trees were commonly planted to replace diseased elm trees because they were hardy and fast-growing, the insect’s effect could be devastating. Sievert said nearly 20 percent of the city’s boulevard trees are ashes.

The emerald ash borer is a green beetle from Asia that has killed at least 10 million ash trees in Michigan, Ohio and Indiana in the last two years. Sievert said the beetle had been infesting trees in Michigan for seven years before it was discovered in 2002.

“It’s not believed to be here in Minnesota, yet,” he said. “We helped the Department of Agriculture check for it this summer. They needed five trees from Minneapolis that could be sacrificed. We chose the trees and girdled them, cutting away all the bark around them, so the tree would die. The Emerald Ash Borer is attracted to a tree in a weakened condition. Later, in early fall, we cut down the trees and they did a sort of autopsy to see if they could find any insects in them.

“If they [the insects] hit a tree, you’ll see tiny holes where they’ve bored in. They lay eggs in galleries that perform girdling under the bark. It takes several years [generally, three to five] for the tree to die. First you’ll notice that it doesn’t look too good. Then you can see exit holes where the borer has come out.”

According to the USDA Forest Service’s web site, adult beetles nibble on ash foliage but cause little damage. It’s the larvae feeding on the inner bark that disrupts the tree’s ability to transport water and nutrients. Sievert said Michigan responded to the crisis by setting up a quarantine area and cutting down every ash tree in a quarter mile radius. “The primary way it moves is by people hauling firewood around. I have a friend in Ohio’s urban forestry department who told me they are imposing fines of thousands of dollars on people who bring in infested firewood. The beetle is already up in Toledo. Right now, from everything we hear at various conferences, it’s not like they have a good handle on it. In Detroit, there are dead ash trees everywhere.”

The Emerald Ash Borer is smaller than a dime but larger than the elm bark beetle, he said. At this point, there is no injection or other form of prevention known to control it. “We’ve dramatically reduced the number of new ash trees we’re planting. About 19 percent of our boulevard trees are ash; we figure that’s about 200,000 trees.” Sievert said they’ve been planting oak, river birch and Ohio buck eye trees instead of ash trees.

“Another pest that’s already here is the gypsy moth,” he added. “The gypsy moth likes oak trees. We sprayed for it in the spring of 2002 to slow its progress. Some time in the next 10 to 15 years, we’ll all be living with the gypsy moth.”

Mike Schommer, communications director for the Minnesota Department of Agriculture, said Emerald Ash Borers are harder to detect than gypsy moths, “because you can see the moths’ caterpillars on leaves.” The Department’s monitoring has ended for the year, he said, and no ash borers were found. But Minnesota is still on alert because of its proximity to states the emerald ash borer has already invaded. He said infected nursery stock and fire wood remain the most common way the ash borer has spread. “People should buy their firewood locally and burn it locally.”

Melissa Brewer, public information officer for the Ohio Department of Agriculture’s emerald ash borer program, said that the beetle has been found in approximately 12 counties in Ohio. “We’re not as bad as east Michigan, where they have 15 million dead or dying ash trees. We are following an eradication protocol of marking every ash tree within a half mile of an infected tree and cutting it down. The tree is chipped into pieces smaller than an inch; that kills the larvae. We’ve been monitoring one site in Franklin County that was found to be infested in 2004 and was eradicated. We’ve been monitoring the effort, and so far it looks like it’s been successful.

“The research [on how to control it] has been going on non-stop since 2002. Before that, the pest was unknown in North America,” Brewer added.

According to the Ohio Department of Agriculture’s web site (www.ohioagriculture.gov), the state has received $16 million from the federal government in the last two years to control the emerald ash borer and state forestry workers have destroyed more than 50,000 ash trees in Ohio so far. There are 55 employees working in the emerald ash borer program.

Information on the Emerald Ash Borer can be found on www.emeraldashborer.info, a collaborative web site established by the USDA Forest Service, Michigan’s Department of Agriculture and Department of Natural Resources and three universities. The Minnesota Department of Agriculture’s web site is www.mda.state.mn.us. Ralph Sievert can be reached at 612-313-7735.