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May 14, 2009, St. Paul, Minn. -- The Minnesota Department of Agriculture today announced the discovery of an emerald ash borer infestation in St. Paul just northeast of the intersection of Interstate 94 and Highway 280. This is the first detection of the destructive tree pest in Minnesota. Read the full MDA press release. Watch DNR video footage of the infestation site.

Photo of emerald ash borers.

Big Trouble for Ash Trees

The deadly emerald ash borer, native to eastern Asia, is coming to Minnesota. The bug lays its eggs on the bark of ash trees. The larva bores into live wood and emerges as an adult, leaving a D-shaped exit hole in the dying tree.

By Mary Hoff

Jacob Ryg has seen plenty of tree troubles as the city forester in Rochester. But the one that really has him quaking in his boots is the one he hasn't seen -- yet.

"It's an environmental disaster, in my opinion," he says. "When it hits Minnesota, we're going to have a huge problem."

The trouble Ryg is talking about is the emerald ash borer, an invasive insect from Asia first discovered in Michigan seven years ago. Larvae of this shiny beetle tunnel beneath ash tree bark, gnawing away at living tissue until they kill the trees -- without fail.

No one has yet found emerald ash borer in Minnesota. But with the assistance of people who inadvertently move larvae-infested wood or trees from one place to another, the insect is spreading rapidly around the Midwest. Experts agree it's only a matter of time before the beetle shows up here too.

For Ryg, that's bad news. One-fourth of the trees lining his city's streets and peppering its parks are ash. When emerald ash borer arrives, Rochester not only will lose the beauty and shade those 17,000-plus trees provide but also will have to foot a monumental bill for removing dead trees and planting new ones.

Multiply that by the entire state, and Minnesota has trouble many times over. Some 3 million ash trees grace lawns and boulevards of our cities and towns. Ash trees are a common component of farmland windbreaks, shelterbelts, and lowlands across southern Minnesota. They are a prominent feature of northern forests. Statewide, 937 million white, green, and black ash trees are vulnerable to emerald ash borer.

"The insect is a tremendous tree-killer," says Steve Katovich, forest entomologist with the U.S. Forest Service Forest Health Protection unit in St. Paul. When ash borers invade an ash stand, tree mortality approaches 100 percent, as abundant beetle larvae munch their way en masse around the insides of trees, girdling and killing them within one to three years. More than 30 million American and Canadian trees already have died as a result.

By taking care not to transport emerald ash borers, Minnesotans can help stave off these invaders as long as possible. Then foresters will have time to plant trees today that can stand in for fallen ash tomorrow. And researchers will gain time to investigate treatments. The sooner we act, the better off Minnesota's streets and forests will be when this ash-eating insect finally invades.

Discreet and Devastating

For decades ash trees (Fraxinus spp.) have been mainstays of the upper Midwestern landscape. Planted in abundance in the wake of the 1970s Dutch elm disease epidemic, they are fast-growing, adaptable, and relatively invulnerable to the various traumas that try trees.

Or so we thought.

In 2002 Michigan State University scientists studied tiny insects that were emerging from beneath the bark of sickly ash trees in southeastern Michigan. The size of a grain of wild rice with the green sheen of a hummingbird, these insects were nothing they had ever seen before. Entomologists at the Smithsonian Institution in Washington, D.C., were equally baffled. It wasn't until an eastern European expert got hold of a specimen that its true identity emerged: an Asian insect known in English only by its scientific name, Agrilus planipennis. This foreign species had likely hitched a ride from China to Michigan sometime in the 1990s in wooden crates or pallets carrying imported goods. The scientists proposed the name "emerald ash borer" in recognition of its jewel-like appearance and its behavior.

But this species was no jewel. Discreet as they are devastating, these deadly invaders lurked beneath the bark of ash trees for years, eating them alive from inside, before anyone detected their presence. As a result, by the time Michigan figured out what the problem was, the problem wasn't just Michigan's anymore. Inadvertently aided by humans hauling infested firewood and shipping infested saplings, emerald ash borers were already hopscotching across states.

In 2003 foresters found the insects in Ohio. The following year ash borers showed up in Indiana. They popped up in Illinois and Maryland in 2006, Pennsylvania and West Virginia in 2007. Last summer they were detected for the first time in Missouri and Virginia -- and our neighbor, Wisconsin.

Lost Goods and Services

Emerald ash borer is not known to be in Minnesota as of this writing. But all it will take is one person bringing larvae-riddled firewood home from the family farm by Milwaukee or bringing an infested sapling dug from a friend's yard near Chicago, and then our emerald ash borer-free days will be gone forever.

"We know it will be here eventually," says Mark Abrahamson, emerald ash borer program coordinator for the Minnesota Department of Agriculture and head of the state's emerald ash borer readiness team.

When the borers do arrive, they'll have plenty to eat. White ash grows in southeastern Minnesota. Green ash grows statewide, especially along streams. Green ash was widely planted for shelterbelts in rural areas, as well as for shade trees in yards and along boulevards in cities and suburbs. Black ash trees are a major component of the hardwood stands lining northern wetlands. Together, these trees create a web of corridors the borer can use to spread.

When ash borer adults emerge from a tree, they usually only fly a couple of hundred yards to another tree to lay eggs. Though they don't fly far, they do fly in abundance, and there is little tree experts think they can do to stop its inexorable spread.

"I don't know if there's really any comparison," says University of Minnesota entomologist Jeffrey Hahn. "The closest probably is Dutch elm disease. . . . This has a potential to certainly be more injurious, more devastating than that."

Odds are Minnesota will lose most, if not all, of its ash trees. We'll also lose the goods and services these trees provide. For example, city trees bestow beauty, cut energy costs, and absorb and filter storm water -- services estimated to be worth over $290 million to Minnesota communities each year. Minnesota ash trees typically supply between 30,000 and 40,000 cords of wood each year, mainly for pulp and paper, but also for firewood and specialty products such as cabinets, furniture, and veneer.

Unique characteristics of black ash have made it a staple of the traditional American Indian basket-making industry, which has already lost access to wood in infested areas. "If and when emerald ash borer gets to the remaining stands, the material will be very rare or nonexistent in some areas," says U.S. Bureau of Indian Affairs forester and basket maker Michael Benedict. "That would have a big impact on the ash basket making that's been with a lot of the tribes for thousands of years. That would pretty much end that particular art form."

Most worrisome for University of Minnesota forest ecologist Lee Frelich is the impending loss of the hundreds of millions of black ash trees that line wetlands in forests north of Hinckley. When the beetles destroy those trees, Frelich says, they will forever change the face of wetlands in northern forests -- habitat for wildflowers, butterflies, songbirds, herons, owls, woodpeckers, moose.

"Black ash swamps are . . . a unique habitat for plants and birds and so on that otherwise wouldn't be there," he says. "We might lose that whole forest type."

Slow the Spread

With the inescapable arrival of emerald ash borer, it's tempting to throw up our hands in despair. But action today could dramatically alter the outcome tomorrow for our state's urban forests and rural woodlands alike.

"The biggest issue right now is to keep it out of here," says Katovich. Fending off emerald ash borer as long as possible, he says, will give municipalities, homeowners, and forest managers time to plant other tree species and get them growing before the ash disappear. And it will give scientists more time to identify and perfect strategies for protecting ash trees, such as introducing parasitic wasps that help keep emerald ash borer in check in Asia or perfecting pesticides that could be used on a limited basis to save particularly valuable individual trees.

"We're hoping by the time it gets here we are able to take advantage of all the research that's going on," says Department of Natural Resources Forestry entomologist Val Cervenka. "The longer it takes [to arrive], the longer we have to pull together our resources and implement our plans for response."

To limit the insect advance, the U.S. Department of Agriculture has placed restrictions on moving firewood, ash trees, and ash tree parts from infested areas. Chippewa and Superior national forests have banned transportation of firewood from out of state, and Voyageurs National Park and some counties are allowing only DNR-approved wood within their boundaries. In 2007 the state Legislature made it illegal to bring firewood onto state land unless purchased from a DNR-approved vendor.

"The best option to slow the spread is to really limit that artificial movement," Abrahamson says. "Emerald ash borer on its own is going to move only a short distance each year."

Find It Fast

Once emerald ash borer does arrive, Katovich says, the sooner we detect its presence, the better.

"If we don't find it for a number of years, that allows it to get really well established," he says. "We might actually have a chance to do something if we find a smaller spot relatively soon. . . . If it's very, very early, we can still try to eliminate it."

In cities and near campgrounds and nurseries, forest managers have been stripping a circle of bark from selected ash trees (borers like stressed trees best) and watching them for signs of infestation. In strategic parts of the state, emerald ash borer surveillance teams have also hung hundreds of sticky purple traps (borers like purple too), which are baited with a chemical that smells like sick ash trees.

Across Minnesota, more than 800 state-certified tree inspectors and several hundred tree care and woodland advisors are watching for the pest. In addition, the DNR, the Department of Agriculture, and the University of Minnesota have trained a statewide network of over 300 "first detectors" to look for signs of emerald ash borer. They also respond to calls from citizens reporting sightings or signs of emerald ash borer to the Arrest the Pest hotline.

Life cycle

Emerald ash borer starts out as a flat, rust-colored egg, just a smidge bigger than the period at the end of this sentence. A single female will lay 80 or so at a time on the bark of an ash tree in summer.

A lanky white larva emerges, burrows into the bark, and begins eating the living wood. In the process, it cuts off the conduits that carry water and nutrients from roots to leaves and sun-made sugars from leaves to the rest of the tree.

In spring the larva morphs into a pupa. In early summer the pupa develops into an adult beetle. Two to three weeks later, the insect bores out of the bark, leaving a telltale D-shaped escape hole. The emerald-colored adult flies off to mate and begin the cycle again.

Trees can survive for two to three years until borers finally push them past their tipping point. Enough larvae, enough serpentine trails, and the flow of water and nutrients inside the tree is completely severed. Twigs, branches, and ultimately the whole tree die.

What Next?

Forest managers are still strategizing the best way to get ready for the invasion. Some are in favor of stepping up harvest of marketable ash trees. Others worry that large-scale cutting of black ash would disrupt the hydrology of the wetlands in which they thrive.

"The concern is swamping these areas by suddenly removing the tree cover that is acting like a water pump," observes Alan Jones, DNR Forestry silviculture, lands, and roads supervisor.

The DNR is developing a ?preparedness plan so the agency can respond in a timely and appropriate manner. "Our state nurseries are no longer growing ash," Jones says. When ash stands come up for harvest as part of a normal logging cycle, the woods likely will be managed for other species.

What species would thrive where ash have sunk their roots for centuries?

"Therein lies the challenge," Jones says. "We're not sure yet. . . . There may not be real good, easy alternatives."

For woodland owners, Abrahamson recommends a wait-and-see approach. "In the normal course of forest management you might want to, if it makes sense with your other goals, reduce your abundance of ash," he says. "But I wouldn't advise anyone making a radical change purely because they're worried emerald ash borer is going to get into their wood lot."

For municipalities, on the other hand, action is in order because thousands of lifeless, leafless, and dangerous dead ash will blow out routine maintenance budgets. Although emerald ash borer may take several years to finally kill a tree, once it does the tree branches and limbs dry quickly. Such brittle trees are much more dangerous for tree workers and nearby buildings, and removal costs skyrocket, DNR community forestry coordinator Ken Holman says.

Minneapolis forestry program manager Jim Hermann helps oversee 38,000 boulevard ash trees, which will cost an estimated $27 million to remove and replant. He is looking at options for using cut ash, from burning it for energy to turning it into marketable products. In Rochester, Ryg stopped planting ash in 2002. Today, as he prepares for an ash-free future, he's working hard to incorporate other lessons of the past.

"We learned from Dutch elm disease that we should plant multiple species, but we didn't plant enough," he says. "We replaced elm with five species. Now we're going to 10 to 20 different species." Maples, lindens, and honeylocust have all been overplanted in the city, and Ryg says he is hoping to diversify the city's trees by planting unconventional species. Top on his list: Kentucky coffee trees, disease-resistant elms, and hackberry.

Abrahamson says that's a good rule for the rest of us to live by as well. If your ash trees are healthy, he says, there's no need to do anything now. But if they're starting to fail, it might make sense to start replacing them with diversity in mind.

"Don't think, 'If I plant all maples I'm safe.' The key is to plant a diversity of trees," he says. "Everything has its bug that's living in another country that could come here. The key is, plant lots of [different species of] trees."

Ash Borer update

At press time, experts confirmed the discovery of emerald ash borer along the Wisconsin banks of the Mississippi River 20 miles south of La Crosse. Learn more at Minnesota Department of Agriculture.

What can I do?

Use only local firewood. To avoid being an insect taxi, buy or cut firewood where you'll burn it. Find a list of approved vendors.

Watch. If you see an ash tree with D-shaped exit holes or lots of dead branches and sprouts from the trunk, call Arrest the Pest, 651-201-6684 or 888-545-6684.

Don't panic. If you want advice on your ash trees, choose an International Society of Arboriculture (ISA)-certified arborist or tree inspector.

Do ponder. Consider planting saplings of another species that can take over if you eventually lose your ash. Find DNR information on tree planting, grants, or visit University of Minnesota forestry for more suggestions on trees and shrubs that aren't susceptible to the ash borer.

Save seeds. Scientists are collecting ash seeds for the National Center for Genetic Resources Preservation in Colorado. To learn how you can help, visit

Spread the warning. Share this Minnesota Conservation Volunteer magazine story with friends and neighbors. Learn more at and Minnesota Department of Agriculture.

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