At-risk ash trees become sad topic in Greenfield and West Allis

Experts offer homeowners advice of what to do about bug infestation

A Wachtel Tree Science worker does soil injection work around an ash tree.

A Wachtel Tree Science worker does soil injection work around an ash tree.

Sept. 3, 2013

With the latest local discovery of the destructive emerald ash borer, city foresters in West Allis and Greenfield expect a flood of calls from homeowners worried about their ash trees.

Greenfield faced the rush first, with the confirmed sighting of the beetle in February. West Allis joined the list of area communities — including nearby Franklin and Greendale — in August, when the insect was found in the DNR section of State Fair Park.

The borers' onslaught is so ferocious that the only ash trees left will be treated ones, judging by other communities' experiences with it, Greenfield forester Dennis Fermenich said. The pest, whose larvae feeds on inner tree bark and deprive a tree of nutrients, takes the green ash trees first, then sweeps back to kill the white ash, he added.

Although the borer hasn't been confirmed in all Milwaukee County communities, homeowners should assume it's around because it generally goes undetected for years, Fermenich said.

Action now

Regardless of when the beetle is found, the advice still remains the same for anyone worried about the species of tree that has been a staple of residential landscaping as well public spaces for decades.

Local foresters and other expects advise homeowners not to wait in deciding whether to treat the tree.

By the time they see the notable D-shaped hole in the trunk through which the emerald ash borer exits, it's already too late, said Fermenich, explaining that the borer starts its infestation at the top of the tree.

Emerald ash borer devastation happens quickly once a saturation point is reached, Fermenich said. It takes the borer about nine years to kill 20 percent of ash trees in a community but after that it takes 20 percent a year until all the ash trees are either gone or being treated.

Because treatments are expensive, homeowners should decide which trees to treat and which to let go and replace with other varieties, Fermenich said. Those that have lost half their leaves cannot be saved, according to emerald ash borer research.

"If they are worth saving, they should be protecting them right now," he said.

Fermenich recommended a Purdue University emerald ash borer decision guide. The site also has the latest research and information, he said.

West Allis forester Michael Rushmer suggested another resource, a University of Wisconsin-Extension publication for homeowners. It can be found online at


Types of treatment

Treatments are of two kinds, but only a professional injecting trunks with emanectin benzoate has proven reliably effective, according to researchers from five universities who have published a multistate paper.

"In several intensive studies conducted by (Michigan State University) and (Ohio State University) researchers, a single injection of emamectin benzoate in mid-May or early June provided excellent control of EAB for at least two years, even under high pest pressure," the researchers wrote.

Other treatments have provided widely varied excellent-to-poor control. Researchers are still studying why the same preparation works sometimes and not others.

For trees of 45 inches around the trunk or less, homeowners can generally get good results by mixing water with preparations containing imidacloprid, available at local garden centers for about $22. This is most effective when applied between April 1 and May 15, according to the Purdue University decision guide. The treatments are good for a year.

But for larger trees, the researchers say homeowners should consider professional treatments.

Trunk injections with emanectin benzoate, the only known substance providing protection for two years, could run in the neighborhood of $150 and $195 for trees 45 inches around or with breast height diameters (which is how arborists look at trees) of 15 inches. A tree that's 75 inches around at chest height could cost $250 or $360 to treat with emanectin benzoate.

Arborists also can inject the soil with imidacloprid in amounts homeowners are not allowed to use. Such injections are 80 percent effective, said David Scharfenberger, president and an owner of Wachtel Tree Science of Merton, which serves West Allis and Greenfield. Soil injections are $122 for a tree that's 45 inches around, but have to be repeated annually, so it's more expensive than the trunk injections.

Costs of treating should be measured against the cost of cutting a tree down, experts suggest.

A big tree can cost anywhere from $300 to $2,000 to cut down, arborists said. It all depends on their location — if they are surrounded by other trees, if they are near buildings and how far debris has to be hauled out, said Jesse Ziemienski, owner of American Tree Experts of New Berlin.

Tree ID tips

Homeowners who don't know if s tree is an ash can go to the Boerner Botanical Garden between 10 a.m. and 2 p.m. weekdays in September, where master gardeners staff a UW-Extension office. Homeowners should bring twigs with leaves or photos or anything to help with identification.

Ash foliage is fairly easy to identify because it has compound leaves with as few as five leaves and as many as 11, but always an odd number, said Sharon Morrisey of the UW-Extension. Further, the leaves are right across from each other on the stem, which is different than most other leaves that normally alternate up a branch, she added.

Identification help is available at or by calling the UW-Extension office, (414) 256-4600.

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