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Summer 2010 Vol. 18 No. 3

The emerald ash borer is here—now what?

The s-shaped galleries underneath the bark are a sign of
emerald ash borer
Photo courtesy of Minnesota DNR

More than decade after the emerald ash borer hitched a ride from Asia to Michigan, the tiny invader is prepared to wreck havoc on millions of ash trees in Minnesota.

The destructive insect was discovered on May 13, 2009, on private property in St. Paul. In February, it was confirmed a half mile away in Minneapolis’ Prospect Park neighborhood. Since then, St. Paul has removed 100 to 150 infested trees and another 400 or so declining ash, in some cases taking out whole blocks. Minneapolis has cut down 48 trees.

The ash borer was also confirmed on April 28, 2010, at a site in southeastern Minnesota across the Mississippi River from an infested stand of ash near Victory, Wis.

With more than 937 million green, white, and black ash trees in Minnesota, including 3 million in cities and towns, communities need to start preparing now for the emerald ash borer, said Mark Abrahamson, emerald ash borer program coordinator for the Minnesota Department of Agriculture.

What you can do

Plant a tree

If you have space in your yard to plant a tree, think about planting one. If you have an ash tree in your yard, planting its replacement will give it a chance to start providing shade.

Prune your ash tree only in the fall or winter

The emerald ash borer is active now, and moving infected wood helps spread the pest. Prune your ash tree only when the beetle is dormant, after Labor Day and before May 1.

Look for symptoms of emerald ash borer infestation

Woodpeckers are the most obvious sign of emerald ash borer in a healthy-looking tree. Look for 1/8 inch, D-shaped exit holes in trees. These are the result of borers leaving the tree once they have become adults. The beetles also split the bark, create s-shaped galleries underneath the bark, and thin the tree’s canopy.

Consider insecticides carefully

Insecticides can effectively protect ash trees from EAB, but trees need to be treated regularly (every one to two years) for the life of the tree. Trees exhibiting more than 50 percent canopy decline are unlikely to recover even if treated. Do not apply insecticides to ash trees out of the likely range of emerald ash borer (a 10- to 15-mile radius).

Obey the quarantine

Hennepin, Ramsey, and Houston Counties are part of an emerald ash borer quarantine. Firewood and any part of an ash tree, including lumber and branches, are not allowed to leave the counties, to help slow the spread of emerald ash borer to other areas.

Report it

If you think an ash tree is infested with emerald ash borer, report it at 651-201-6684 or

(Sources: City of Minneapolis, University of Minnesota Extension)

“What we have found is that we’re consistently lagging behind discovering this insect when it gets to an area,” Abrahamson said at the 2010 Minnesota Spring Maintenance Training Expo in St. Cloud. “There’s usually a two- to five-year lag from when the insect gets to an area and when it’s discovered. So we have to expect there are places, even in Minnesota, where it’s present and we don’t know it yet.”

Other states that have battled the emerald ash borer have found that “waiting and doing nothing is more expensive,” Abrahamson said. “They found in Michigan when you have dead standing trees, it’s a threat to wires and buildings.” He said the brittle, dead trees are also more dangerous to remove.

Epicenter, St. Paul

Entomologists believe the emerald ash borer hitched a ride on a ship from China or the Koreas in the 1990s. It was first discovered in Detroit in 2002 and has since spread to at least 13 states.

The ash borer probably reached St. Paul in 2006, Abrahamson said. Three years later, it was discovered by a Rainbow TreeCare worker trimming trees in the St. Anthony neighborhood of St. Paul, close to the border with Minneapolis.

The worker saw the distinct S-shaped galleries on a sickly tree. EAB was confirmed the next day by federal laboratories.

The city swung into action. With help from the state Department of Agriculture, workers began a survey of all ash trees near the infestation site in St. Paul and Minneapolis, checking for thinning tree crowns and woodpecker damage, two telltale signs of EAB. In St. Paul, they found the core infestation was contained to the original area where EAB was discovered, said Rachel Coyle, St. Paul’s emerald ash borer program coordinator.

Because the ash borer starts to emerge from trees in early June, the city immediately began cutting down suspect trees on public and private property—including 15 on one property alone.

“Stumps were immediately ground out. All of the material had to be chipped before [it was] brought to a processing plant because of the emergence,” Coyle said.

The city council approved an emerald ash borer management plan on June 17, 2009, but the plan remained unfunded for several months. In February 2010, a new nuisance ordinance was approved that allows city employees to condemn private property trees known to be infested with EAB.

“In retrospect, it would have helped if we had a plan before we found EAB,” Coyle said.

In early June 2009, the city girdled 20 trees near the infestation site as trap or sink trees. Those trees were later removed and 17 were found to be infested, Coyle said. Workers girdled another 21 trees in early 2010.

“We’ll probably continue with that for as many years as there are ash trees in that area just to keep knocking back the EAB population in that area,” Coyle said.

The city also began destructive sampling in fall 2009. Fifty-eight public trees were removed; 3 were found to have EAB. The most distant infested tree was on the University of Minnesota’s St. Paul campus, a mile from the original site.

In fall 2009, the city tried a pilot program to remove 37 ash trees on two blocks that had been damaged by previous street work. In February and March, workers took out 520 trees as part of a structured removal program.

“We split removals up among council wards,” Coyle said. When the removals started in the city’s blue-collar northeast, she got calls asking when she would be removing trees in a more affluent neighborhood. “People thought we were staying away, targeting poor neighborhoods, so I was able to say we’re starting there in fall.”

Helping cities prepare

The D-shaped exit holes
Photo courtesy of UKY College of

In one sense, having the first emerald ash borer outbreak in the state helped St. Paul. The city was able to get $722,600 from the state’s Outdoor Heritage Fund to help with tree removal and replacement because slowing EAB is a statewide priority.

As of April, St. Paul had spent “less than $100,000” of its own money to remove and replace trees, Coyle said at the conference.

But for other cities, cost is a huge unknown. At a time when municipal budgets are stretched thin, a major tree replacement effort is a painful budget hit.

Abrahamson, head of the state’s emerald ash borer readiness team, said this year the state had a pool of money to help cities fight the emerald ash borer and there were some federal funds as well.

The state Department of Agriculture received $2 million to help communities prepare for EAB. Half of that money, $1 million, was spent on communities with confirmed EAB infestations—at the time, St. Paul, Falcon Heights, and the University of Minnesota’s St. Paul campus. The rest was spent by the department on outreach and to help communities that did not yet have a confirmed infestation prepare for EAB.

But Abrahamson said he’s not sure about future funding. “That’s the kicker, where will the money come from to fund this?” he said.

That’s another reason it’s important for cities to plan ahead. “Inventories are a must,” said Ken Holman, program coordinator in the Department of Natural Resource’s Forestry division. Many city employees don’t feel they have the skills, time, or equipment to maintain a tree inventory. But without one, cities can’t quickly respond when their ash trees are threatened.

The DNR is currently updating a rapid assessment survey of all common genera of trees for 700 communities in the state. The results will be available later this year, he said.

At the same time, six cities—Detroit Lakes, Hibbing, Morris, Hutchinson, Hendricks, and Rochester—are piloting a new method for rapid sampling of street tree populations. The new technique takes about 120 staff hours to sample 2,300 trees, Holman said.

“We’re setting up these cities as models for how you go about inventorying, how you develop outreach to the public, and how you might share resources with the public,” he said. “This helps communities go through the process of preparing an EAB readiness plan.”

The state also has resources online, including draft EAB guidelines, a Purdue University cost calculator, and information about interactive tools to help city employees replace lost trees with a more diverse streetscape, Holman said. (See sidebar below.)

Abrahamson said Minnesota has learned lessons from the states to the east hit by emerald ash borer—including Michigan, Ohio, and more recently, Wisconsin and Iowa. One of the challenges of the emerald ash borer is its slow destruction of trees. Because the tree doesn’t die immediately, signs of infestation are difficult to spot. By the time EAB is discovered, it has spread far beyond its initial infestation site.

“What they saw in Michigan and what we’re likely to see here is that you have this period, the establishment phase of EAB. The population is growing, but slowly. Then you reach a tipping point where the population is growing rapidly but also spreading rapidly,” he said. “In Michigan, you had the first dead trees appearing, and then it takes off like crazy, you have lots of EAB in a short time and lots of tree mortality in a short time.”

Holman offered these suggestions for cities trying to plan for EAB:

  • Define roles: Who is going to be the go-to person on emerald ash borer questions?
  • Start planning early. Have plenty of materials, print and online.
  • Have a Web “front door” with local information and links to an ash borer diagnostic tool.
  • Brief your city council on the value of healthy trees and the cost of inaction. The state has a “Trees Pay Us Back” campaign to put a dollar amount on energy savings and stormwater mitigation that trees provide.
  • Form partnerships with neighboring communities to share equipment and pool resources.

St. Paul’s lessons

John Lloyd of Rainbow TreeCare said many companies are trying to take advantage of the public’s lack of knowledge and worry about the emerald ash borer.

“A lot of national firms are looking at this as a profit center. Nothing is more profitable than the demise of something people care about,” he said.

That puts the burden on cities to educate residents about how to identify and slow the spread of the insect, he said.

In the year since the emerald ash borer was discovered in St. Paul, Coyle said she’s learned that public relations is 90 percent of her job.

The city’s first community forum on EAB was its largest. Since then, the city has a more modest turnout for its community events. In winter 2010 the city distributed pamphlets to 400 households. Two people attended a city forum. Coyle then direct-mailed postcards to 170 households. Five to six people came to a second forum.

“So far, we’ve had a pretty low turnout. I don’t know if that’s good or bad,” Coyle said. “From the standpoint of we’re cutting down all your trees, we don’t have a lot of people yelling at us, that’s good, but as far as doing that outreach at that time, it’s not good that people aren’t coming.”

Abrahamson and Coyle organized emerald ash borer field days, using downed trees for hands-on activities. Attendees could scrape bark off trees, identify the S-shaped galleries, and even take a larvae home if they found one.

A big question for the city was whether it should use pesticides to try to save trees. “Historically St. Paul has been anti-pesticide use,” Coyle said. “I know from talking to a lot of homeowners it’s true. There are concerns about long-term use of insecticides to save ash trees, and, on the other side, concerns about losing trees.”

St. Paul set up a permit program to allow residents to treat trees in public spaces—if they get a permit from the city and use a licensed tree-care company.

The city has not yet used pesticides on any infested trees, Coyle said, although it is considering it on a small number of trees in 2011. One issue is public perception.

“If we treat one tree and girdle another, homeowners might wonder why. We really need to work with homeowners and have them understand why we’re doing what we’re doing,” she said.

Coyle recommends that public works departments create a Web site, “even if it’s just links to different resources.” She also says cities should work with volunteers, community groups, and schools whenever possible.

“People really need to feel like they’re part of the process,” she said.

Hope for the future


The three Web sites below have a range of helpful materials and links, including ash borer identification tips, a tree care company register, and recommended trees for Minnesota.

Research continues into emerald ash borer pests, such as a parasitic wasp that has been tested in Michigan. There’s also some research that has found the ash borer doesn’t thrive in cold areas, Abrahamson said.

“There’s some encouraging data that particularly northern Minnesota isn’t going to be a real hospitable place for EAB,” he said.

St. Paul’s early and aggressive response to EAB might also help slow the spread of the ash borer in Minnesota, he said. “We found that tree in St. Paul two years faster than any other part of the country. That bought us two years to plan and train,” he said. “If we can reduce population numbers in this part of the buildup, perhaps we can also push back these tipping points in the future.”

If communities in Minnesota are able to act quickly and keep the emerald ash borer population low, the state could be an exception to the insect’s trail of tree devastation. But, Abrahamson said, at this point, “There’s a lot we don’t yet know.”

—Trisha Collopy, LTAP freelancer

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