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State on the trail of the emerald ash borer—and on the offensive

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FRANK J. SCHULTZ
April 26, 2010

Look at the map of the invasion, and you’d think Wisconsin has dodged a bullet.


The invader is the emerald ash borer, which kills ash trees wherever it goes. It’s been found only in a few spots in the Badger State.


So far, most of the state has been spared. But the map might be deceiving.


Consider the 10,000 acres of infested land in Ozaukee and Washington counties. Ash borers were discovered there in 2008, but the area is believed to have been infested for three years without being discovered, said Jennifer Statz, who heads up state programs that combat EAB and other pests that are invading our forests.


So what other areas of the state already are hosting the destructive beetles but simply haven’t been identified?


Intelligence work

State workers in May will be hanging purple ash-borer traps around the state. Rock County will be blanketed with the traps because of the state line and Interstate 90/39.


Interstate highways might be the main invasion routes. The insects themselves don’t fly very far, but scientists say insect larvae hitch rides on the firewood that humans transport when they head to the great outdoors.


Anyone familiar with I-90/39 knows it’s a major road for people from Illinois heading north. Large parts of Illinois are infested with emerald ash borer.


So far, Wisconsin has two known infestation areas—the one in Ozaukee and Washington counties and another tract of more than 20,000 acres along the Mississippi River in Vernon County.


But emerald ash borers have been found in two other locations, one in Kenosha County and one in Green Bay. In each of those cases, a single beetle was found in one of the purple traps, both last summer.


Wisconsin forests contain more than 770 million ash trees, nearly 7 percent of the tree population. Ashes make up an estimated 20 percent of the state’s urban trees.


It is estimated that ash borers have killed or are in the process of killing more than 50 million ash trees in the Midwest, and they aren’t done yet.


Undercover operatives

Ash borers burrow into ash-tree bark. They don’t like any other kind of tree.


They usually emerge around Memorial Day in Wisconsin, but they might come out earlier this year because of the warm spring, Statz said.


The beetles are programmed to find ash trees. They burrow under bark and lay eggs, which soon hatch little white worms, called larvae.


The larvae spend the summer eating the layer between the bark and the wood, weakening and—sometimes over several seasons—killing the tree.


Larvae winter under the bark and turn into beetles that chew their way out in the spring.


The firewood front

One positive sign is public awareness, Statz said.


Statz each winter sets up a booth at boat shows, hunting shows and similar shows, telling outdoor enthusiasts about invasive species.


In the past, awareness was rather low, but “every person I spoke with this year had at least heard of emerald ash borer and had heard about concerns regarding the movement of firewood,” Statz said.


Statz said DNR surveys have found a similar increase in awareness over the past few years.


The state firewood rule is changing, by the way. Until now, no state parks and other properties would allow firewood from farther than 50 miles away from the campsite. Now, it’s 25 miles, and that has been extended to national forests in northern Wisconsin as well.


Civilians can help

Statz noted that pulp mills, loggers and nurseries have operated under state and federal regulations for decades, so adding on the ash borer restrictions was simple enough for them.


Firewood is still in the wild-West stage compared with other wood products. Bundles are for sale at big-box and convenience stores and are not required to be bug-free.


Statz said to look for a label or sticker that says the wood is state-certified. That means it’s been kiln-dried or “seasoned” for at least two years.


Firewood sellers are not required to get their product certified, but Statz expects regulations to tighten, making it increasingly difficult to sell non-certified wood.


Statz notes that firewood rules don’t protect only ash trees. Dutch elm disease, gypsy moths and oak wilt are some of the pests and diseases that hitchhike in firewood.


On the offensive

Wisconsin’s strategy is to identify EAB infestations, contain them and work with landowners to remove the emerald ash borer habitat. That means cutting the trees.


“If you can lower the number of ash trees in an area, you reduce habitat for the beetle, which decreases the population of the insect and the spread of the insect,” Statz said.


Scientists are experimenting elsewhere with tiny, imported Asian wasps that feed on EAB larvae. Wisconsin is considering using that tactic, but the wasps probably won’t be introduced here until 2011, Statz said.


The end game

Will emerald ash borer eventually wipe out ash trees in Wisconsin?


Statz is hopeful. She points to stands of ash in eastern Michigan that have inexplicably survived the onslaught. Scientists don’t know why.


And maybe those parasitic wasps will strike a blow against the beetle.


“My hope is that it doesn’t go crazy here,” Statz said.


Or things could go badly.


“Once EAB gets rolling, I am not sure whether biological control can get going fast enough to hold it at bay,” said Phil Townsend, a professor of forest and wildlife ecology at UW-Madison.


And no one really knows how many more outbreaks are already spreading in Wisconsin, as yet undiscovered.


That’s one reason one of Townsend’s students is using satellite imagery to map ash distribution in the forests of Wisconsin.


The maps will help forest managers identify high-risk areas.


“From a science perspective, we are also interested in how the forests are going to change, either post-harvesting or post-EAB,” Townsend said.



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