Staying ahead of the ash borer

The invasive bug is here, and Bryn Mawr is ready

BRYN MAWR — Last September, a group of Bryn Mawr residents spent a day counting every ash tree on every street and in every yard of their neighborhood.

It would be another six months, until February, that emerald ash borer was first found in Minneapolis, infesting a stand of trees in the Prospect Park neighborhood across town. But in Bryn Mawr they weren’t waiting for the bug to come to them.

The tree census was part of a plan to stay one step ahead of the invasive beetle that, experts say, will wipe out most of the ash trees in the country, of which almost 900 million are growing in Minnesota.

“If emerald ash borer does what it’s done in other places, then we’re looking at it as ash trees are going to be history,” said Ralph Sievert, forestry director for the Minneapolis Park and Recreation Board.

The Bryn Mawr Neighborhood Association [BMNA], which formed an emerald ash borer committee last year, provides one example of how neighbors can stay ahead of the problem.

The tree census counted 853 ash trees on public and private property, excluding parks, and noted their location. BMNA will host an information session for neighborhood homeowners this spring to go over options for removal, replacement or chemical treatment of their ash trees.

BMNA Board Member Jessica Wiley, who served on the committee, lives on a section of Newton Avenue that, on older maps, is identified as Ash Street. There, neighbors are facing the potential of a dramatically altered streetscape.

“All of our boulevard trees are ash, down to the last one,” Wiley said.

The problem for the city of Minneapolis is exponentially larger.

A growing problem

Sievert said ash is one of the top-three tree species in Minneapolis, accounting for about 21 percent of the estimated 900,000 trees on public and private property. That’s roughly 190,000 ash trees in the city, and an estimated 38,000 of them line boulevards.

He said the city was preemptively removing “defective or declining” ash trees already, to spread the impact on the city’s urban forest out over time.

“The experts agree that the population of emerald ash borer really starts off slow and then it just kind of takes off, and then ash trees are dying all over the place and you’re just reacting,” he said. “The idea is to try and [remove] as many this way before you’re reacting.”

Infestations have killed tens of millions of trees since the bug was first discovered near Detroit in 2002. As of this winter, infestations were reported in 13 states and Quebec.

Minnesota’s first infested trees were discovered last May in St. Paul’s South St. Anthony Park neighborhood. In November, arborists identified infested trees on the University of Minnesota campus in Falcon Heights.

The Minnesota Department of Agriculture began a tree survey after the initial discovery, working out in concentric circles from ground zero in St. Paul. While the bug often moves into new territory when people transport infested wood, the adult beetles also can fly up to two miles per year on their own, Michael Schommer, the agency’s communications director, said.

That survey turned up the infested stand in Prospect Park, Schommer said.

The adult emerald ash borer, a metallic-green beetle about the size of Abe Lincoln’s head on a penny, eats ash leaves but is relatively harmless. It is far more destructive in its larval stage, when it burrows into the phloem, a nutrient-carrying layer of tissue just beneath the bark.

Woodpecker activity is a telltale sign of emerald ash borer infestation, and one symptom that’s easier to spot now, before trees fill out with leaves. In the spring and summer, thinning foliage at the top of an ash and sucker growth lower on the trunk also may indicate infestation.

When larvae emerge as adults, they leave D-shaped exit holes in the bark of an ash tree. But they are so small even a trained eye might overlook them.

Very active infestations will leave the phloem riddled with S-shaped burrows. In some cases, patches of bark will detach from the phloem in blisters.

Homeowners who suspect an infestation should contact the Park Board or the Minnesota Department of Agriculture, Sievert said.

Planning a response

Sievert said homeowners have several options for dealing with infested ash trees:

• Do nothing. It may be several years before an infestation kills an ash, but the bigger the tree, the more it will cost to remove.

• Plant a replacement tree now. When the ash must be removed, the new tree will have a head start.

• Contact a licensed tree professional and begin chemical treatment. Researchers in several states are testing various insecticides, with uneven results.

While homeowners can pay to treat boulevard trees, the cost of treating all 38,000 boulevard ash is too great for the city to consider a large-scale insecticide plan. Park Board foresters are instead focusing on diversification of the urban forest, Sievert said.

After Dutch elm disease claimed tens of thousands of those majestic boulevard trees, the city began planting a diverse array of replacement trees on a block-by-block basis. Now, they are aiming for a diversity of species even within a block.

The devastation brought by the emerald ash borer may, in a way, leave the city better prepared for the next epidemic. Homeowners, too, should heed the wake-up call, urged Bryn Mawr resident Kathy Ripke, a master gardener who worked on the neighborhood tree survey.

“If there’s a positive — in my head, at least — it’s that as this bug is coming through people will kind of take stock of the trees that are in their yards and how important they are to them,” Ripke said. “Having this vigilance can be good long–term.”

Emerald ash borer resources

For answers to your questions on emerald ash borer, call the Minnesota Department of Agriculture’s Arrest the Pest Hotline at 651-201-6684 or email [email protected] Hotline operators can connect callers with trained first detectors.

The department of agriculture website also includes tips for identifying infested trees and information on various treatment options. Go to and click on “Do I have EAB?”

The U.S. Department of Agriculture, various state agencies and universities have compiled a wealth of information at

The Minneapolis Park and Recreation Board website includes more information for homeowners, as well as an outline of city plans for dealing with the pest. Go to or call the Park Board forestry division at 370-4900.

It is recommended that homeowners considering chemical treatment options contact a city-licensed tree service contractor. For a list of licensed contractors go to