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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

The emerald ash borer, about the size of a grain of cooked rice, has killed more than 15 million ash trees in Michigan, Indiana, Ohio and Ontario. © David Cappaert, Forestry Images
The emerald ash borer, about the size of a grain of cooked rice, has killed more than 15 million ash trees in Michigan, Indiana, Ohio and Ontario.

© David Cappaert, Forestry Images

April 2006

Bundling up the borer

Containing firewood is an important plank in staving off a spreading forest pest.

Michael Skwarok

The latest beetle invasion
How firewood gets its legs
Watching out and planning for a border crossing
Arresting disease in city trees
Keeping an eye on ash
Thumbs-down to firewood hitchhikers

Just as towering elms and spreading American chestnuts were toppled by tiny fungi, so too foresters are concerned that ash trees in the Great Lakes region are threatened by a new tree killer. The emerald ash borer, an imported beetle from Asia, has killed millions of ash trees in southeastern Michigan and in nearby counties of Indiana and Ohio. Infestations have also spread into Ontario, Canada and just last September jumped across Lake Michigan and were discovered at Brimley State Park on the eastern edge of the Upper Peninsula. Other isolated pockets have also spread throughout Lower Michigan's forests and urban landscapes.

Wisconsin foresters and other experts believe it won't be long before the emerald ash borer (EAB) shows up here. And the popular opinion is that when it surfaces, EAB may tunnel into the state under the bark of a piece of ash firewood, the likely cause of infestations in Michigan and elsewhere outside of the ground zero hot spot in Detroit.

Armed with that knowledge, Wisconsin authorities have stepped up efforts to educate the public about pests and diseases harmful to both forests and urban landscapes as well as explaining the transmission route through firewood.

The latest beetle invasion

Emerald ash borer was first identified in the Detroit area in the summer of 2002, though investigators believe it arrived as much as a decade earlier in ash wood from Asia used to stabilize cargo in airplanes or seafaring ships. The beetles' numbers multiplied in that time in a core area of infestation that included six counties. Ash trees began to die and now, nearly four years after EAB was identified, the species is blamed for the deaths of more than 15 million ash trees in Michigan, Indiana, Ohio and Ontario.

Keeping an eye
on ash
Ash trees that are getting weaker (declining) can show the same symptoms from emerald ash borer that they show from several other stress factors and diseases. Nevertheless, if your ash trees show three or more of the signs below, please immediately report these symptoms to the Wisconsin Department of Agriculture, Trade and Consumer Protection at 1-800-462-2803.

  • yellowing crown or branches dying back at the top of the tree

  • a dying tree that sprouts new growth from the trunk or near the base

  • heavy woodpecker activity on the tree

  • the presence of small, D-shaped holes about 1/8" wide<

  • winding tunnels underneath the bark

  • bullet-shaped, iridescent green beetles present from June to August

The adult borer is only one-third to one-half inch long. Metallic emerald green wings cover a bronze, slender, bullet-shaped body. When it emerges in the late spring, it chews a 1/8-inch-wide hole shaped like a capital "D." Adults emerge from mid-May through August and live three to four weeks feeding, mating and laying eggs. A female can lay 60-90 eggs inserting them a few at a time into tiny crevices in ash bark to begin the cycle anew. In cold climates where females may get a late start laying eggs, the larvae may actually stay in that phase for an entire year.

The eggs hatch within one to two weeks, tunneling through the bark into the thin cambium layer just beneath the surface. In this living layer the white, flat larvae grow to about 1 inches and carve out winding, S-shaped tunnels that harm, and eventually kill, the tree. As the infestation grows and the tunnels become more numerous, they cut off the flow of water and nutrients, starving the tree. The borers attack at the top of the tree first, causing dieback at the crown. As adult beetles emerge, they reinfest the same tree, moving down and gradually weakening and killing the host tree within two or three years.

The cost to municipalities and property owners to contain and clear an infested area is enormous. In some places in Michigan, cutting down, removing and destroying trees has run close to $1 million an acre. Homeowners may sometimes share the expense of removing trees from their backyards and boulevards. To contain this disease, removed trees must be either chipped into small pieces that measure no more than 1 x 1 inch or the bark and first half-inch of the underlying wood must be removed and chipped or burned. The remainder of the downed trees can be moved and utilized.

"In its native Asia, the beetle is a minor pest," said Andrea Diss, DNR forest entomologist and coordinator of the agency's gypsy moth program. "Ash species there have evolved with EAB and developed natural resistance. They aren't significantly affected by it."

"But here in the U.S., it's a whole different story," Diss added, "because our trees did not evolve with EAB and the insect has no known natural enemies here."

Efforts to contain EAB in the core infestation area of southeast Michigan have met with limited success. Regulations restrict timber products and nursery stock from moving out of the area, but people are moving infested firewood around the state and beyond Michigan's borders.

How firewood gets its legs

"Anyone with a chainsaw or an axe, and a truck or trailer can get their hands on firewood without too much difficulty," said Melody Walker, plant pest and disease manager at the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP). "Pick up the phonebook and you'll find any number of firewood dealers. This wood moves around here as unnoticed as a milk truck or a boat trailer. It's just part of the landscape."

Firewood is commonly sold at gas stations, supermarkets, roadside stands, state parks and private campgrounds for daily or weekend use in campfires. Some large retail outlets bundle firewood in plastic or bind it with twine; an armful goes for as little as a few dollars.

Firewood has now become the latest target of scientists and state and federal officials concerned over the spread of harmful, usually exotic, pests and diseases that are killing trees in forests, parks and neighborhoods. Regulations and fines aim to prevent firewood movement in Michigan and Ohio where EAB has already spread. Penalties for moving firewood out of EAB containment areas range from $1,000 to $250,000 and jail time of up to five years. Michigan authorities have firewood checkpoints at a number of borders including the Mackinac Bridge and the ferry landings in Muskegon and Ludington.

It's not just the emerald ash borer that concerns foresters and others. Gypsy moth and the two-lined chestnut borer are equally adept at spreading infestations via firewood, as is the fungus that causes oak wilt disease. Gypsy moth is especially transmissible and can move to new locations on just about anything. The female moth lays eggs in late summer in a sticky, hair-covered mass about half the size of a golf ball that adheres to whatever she rests upon at the time. Trees, of course, are common targets, but it's not unusual to find egg masses in the wheel wells of automobiles, boat trailers, children's outdoor toys, camping equipment, picnic tables or lawn furniture.

"Just about anything in your backyard or campsite can play host to a new batch of gypsy moths," Diss said. "If those items are mobile, there's the chance that you could be giving the moth eggs a free ride to a new home."

Watching out and planning for a border crossing

"We've known for a long time that some of these insects and diseases were moving around on firewood," said Jane Cummings Carlson, DNR forest health coordinator. "We try to educate folks and deal with the problem. Emerald ash borer is so costly to manage and so potentially devastating that we have to ratchet up our efforts."

One destination where campers are likely to bring in firewood from unknown sources is the state park system. Beginning in 2006, campers visiting Wisconsin state parks will be dissuaded from bringing in their own firewood and asked to buy campfire wood inside the park or from local businesses just outside the park. Those vendors will be required to show they are only selling firewood that's cut from a nearby source.

Minnesota is considering a similar approach in its parks and other Midwest states will be watching with interest.

"We realize this may be an unpopular policy for some of our guests, but the fact is infested firewood is spreading EAB in Michigan" said Wisconsin DNR Parks Director William Morrissey. "Given last fall's discovery of the beetle in the U.P., it looks like it's only a matter of time before EAB shows up here. We're charged with protecting our public lands to the best of our abilities, and this step will help keep the emerald ash borer out of our public campgrounds for as long as possible," Morrissey said.

"We hope that private and county-run parks and campgrounds will also take a firm position on the sources and use of firewood on their properties," Morrissey added.

Yellowing crown and dead branches in young ashes may indicate infestation. © Richard Rideout
Yellowing crown and dead branches in young ashes may indicate infestation.

© Richard Rideout

Federal properties already forbid the use of ash firewood at Wisconsin campsites within the Chequamegon-Nicolet National Forests and on the Apostle Islands National Lakeshore.

Scientists and regulators in Wisconsin have been working on early detection plans for EAB and are ready to act quickly. DATCP is developing the authority to issue quarantines and restrict wood movement out of counties. In states without such rules, the federal government through the USDA's Animal Plant Health Inspection Service (APHIS) can issue quarantines affecting residents and businesses across the entire state.

The Wisconsin response plan includes comments from the timber and pulp industries, private arborists, Native American officials and local governments. DATCP would lead the response and rely on expertise from various other agencies and professionals.

DNR foresters have been setting traps to detect emerald ash borer since 2004. Forest health experts conducted visual surveys of all state parks that year and "trap trees" were prepared in 12 locations, 10 of them on state forestland. A trap tree has a strip of bark removed and a sticky gel applied above and below the wound. The open wound attracts all kinds of insects – including any nearby emerald ash borers – which would be trapped in the gel as insects deposit eggs on the wounded tree.

With some local assistance, trees at private and county campgrounds in northeastern Wisconsin nearest the area where EAB was found in Michigan are also inspected periodically. In 2005, the survey was expanded to include detection trees along the Lower Wisconsin Riverway and visual surveys at 101 private and county campgrounds in northeast and southeast Wisconsin. A total of 2,447 trees were surveyed last year, including some on national forestland.

"We didn't find any EAB and we learned a great deal about the native insects infesting our ash trees," Cummings Carlson said.

Arresting disease in city trees

Wisconsin's forests contain approximately 717 million ash trees. And in urban settings ash varieties (green and white) are the second most common species behind Norway maples. Ashes grow quickly and do well against such urban hazards as salt runoff from roads. Coincidentally, they are resistant to defoliation caused by the gypsy moth and when Dutch elm disease ravaged many communities, homeowners and urban foresters replaced those trees with ash.

Finding ash borer in city trees could again dramatically change the look of our communities and neighborhoods.

"When an infestation is discovered, it's not just infected trees that need to come down," Walker explained. "To slow disease spread, all ash trees within a one-half mile radius of infected trees are also removed. If an infested woodpile is discovered, authorities would strip bark from several nearby ash trees and monitor them for signs that EAB had spread. If discovered, a more drastic eradication plan would begin. You can see how that would quickly become an issue for more than just the homeowner where the emerald ash borer was found."

Walker is quick to add that new treatments are being studied and Wisconsin's response to an infestation might in the near future look much different from tactics Michigan employed just a few years ago.

Everyone working to contain EAB in the upper Midwest realizes that changing people's habits with firewood is going to take a concerted effort. Many people heat with wood. Some are using outdoor wood-burning furnaces to cut heating costs and many more enjoy a fire in home fireplaces. But most of that wood comes from local sources. Taking firewood to distant campsites appears to be a much more common route for hastening the spread of invasive species like the emerald ash borer.

"Controlling or containing EAB is going to require just a little attention from a whole lot of people," Walker said. "It's not hard work, but we need to change a couple habits and be aware. People need to understand that their actions are an important factor in either containing or spreading insect-borne diseases carried on firewood."

Michael Skwarok is a DNR communicator and educator working on forest pest and environmental issues.

Thumbs-down to firewood hitchhikers
Don't be a carrier. To lessen the odds of transporting emerald ash borer or other forest pests on firewood:

  • Purchase firewood from the same general location where you plan to use it. Local firewood is less likely to introduce new pests and diseases into your neighborhood.

  • When you go camping, leave your firewood behind at home and buy the wood that you need at your campsite or from a nearby vendor. Almost all state-run campgrounds have contracts with local firewood vendors.

  • © Robert Queen

  • If you do move firewood around the state for camping or use at a cabin or second home, be sure to burn up your firewood supply before spring, when pests and diseases begin to emerge. If moving firewood in the spring and summer, store it under a tarp and bury the tarp edges with dirt. Don't leave any unused pieces behind.

  • Only buy or move dry firewood that is free of bark. You will practically eliminate any chance of moving harmful pests and diseases this way, with the exception of gypsy moth egg masses, which could be found on any outdoor surface in an infested area.