EcoMyths: Emerald Ash Borer destroys millions of trees in Chicago and US

April 29, 2013

Alison Neumer Lara

Slash and burn: Why so many trees are cut down in the Chicago area.

Say hello to a small unwelcome guest: the emerald ash borer.

This invasive wood boring beetle has killed tens of millions of ash trees in the US and millions more to come. Cutting down these trees is just one strategy to get rid of the pest and save the remaining ash forest, but as we learned here at EcoMyths Alliance, it’s not enough. For the next segment of our EcoMyths series, Kate Sackman and Jerome McDonnell talk with Peter Gordon, city forester for Lake Forest, and David Horvath from The Care of Trees - both are ISA Certified Arborists.

Emerald ash borer (EAB) is an exotic insect native to China and eastern Asia. The bug hopped a ride to the U.S. in cheap wood packing material more than ten years ago. First detected in Michigan in 2002, today EAB infestation is a problem in 19 states. Most recently in New Hampshire, the state’s department of agriculture confirmed detection on April 5th.

Aside from feeding on leaves, the adult beetles do little harm. Ruin occurs when in larva stage, EAB


chew through trees and damage its vascular system – the tissue right under the tree bark that’s responsible for transporting water and nutrients from the roots to the top leaves and branches.

Scientists say its continued spread across the country is most likely due to the sale of firewood from quarantined areas across state lines. Even worse: Stress from climate change, namely drought, makes the trees more vulnerable to EAB. North American ash trees have no natural resistance to this foreign guest.

Arborists explain with such a large food source for the pests, the problem is only expected to grow. According to one of the nation’s largest tree care companies, The Care of Trees, Ash trees comprise 10 percent to 40 percent of local urban forests. Many ash trees were planted during the recent housing boom – creating a monoculture that makes them easy targets for EAB -- and they are natural reproducers.

So what to do? Initially, many communities took a wait and see approach, says Peter Gordon, city forester for Lake Forest, IL -- where 19 percent of the tree inventory is ash. EAB came to attention during the economic downturn, Gordon notes, and budget-strained municipalities had few resources for tree treatment.

“The strategy was to see how states, count[ies] and towns handled EAB where it was first discovered,” he adds.  “But now we don’t have as many options.”

Indeed EAB is an epidemic and can’t be ignored, says Fredric Miller, a professor of horticulture at Joliet Junior College and a research associate with the Morton Arboretum in Lisle, Ill.

“If you choose not to do any treatment, you will be overrun,” Miller says. “What communities have to come to grips with is that either you are going to manage this on your schedule, or the insect will dictate the schedule.” And that means, in part, cutting down lots of trees in our neighborhoods in an effort to stop or slow the spread of EAB.

Arborists explain the alternative for a badly infested tree – allowing it to die from EAB damage and then cutting it down – is worse, because it does nothing to prevent the beetle from paying a house visit to a neighboring tree. Also, Miller points out, dead ash trees are a dangerous liability and must be removed – they’re structurally weak and can fall during wind or ice storms. Many of these trees line walkways and paths in neighborhoods and forest preserves.

But some trees can, and should, be saved with proper insecticide treatment, explains David Horvath, an arborist in suburban Chicago with The Care of Trees.

Horvath says that homeowners and municipalities are now charged with identifying “valuable” trees – generally larger (greater than 12 inches in diameter) that provide environmental benefits such as shade to decrease energy demand, a deep root system that mitigates storm water damage or simply beauty to the property.

Overall, an integrated approach – treatment, prevention and some targeted tree removal – is the best way to put the brakes on EAB, and avoid destroying urban forest, say Horvath and the other scientists EcoMyths interviewed.

According to a 2011 article in the Journal of Environmental Management, prevention and treatment may make more sense economically, too. The estimated cost of treatment, removal and replacement of EAB in all affected states from 2010 through 2020 is $12.5 billion. Prevention tactics (such as destroying egg-laying EAB and targeted tree removal) could slash those costs by up to $7.5 billion, the authors concluded.

In the Chicago area, for example, municipalities spend up to $1,100 to remove and replace one tree, according to a 2012 survey conducted by Miller and his team.  He notes that the same tree can be treated with insecticides for more than 50 years at the same cost.

Insecticides may sound nasty, but remember the alternative: cutting down the tree or letting it die anyhow, while giving that nasty beetle a free pass for its next meal. Plus, when used correctly and responsibly, experts say, insecticides targeting EAB are not likely to harm humans or the environment.

How else are government and science addressing the spread of EAB? Interstate regulation prohibits the sale of firewood from quarantined areas. Also any wood packing material used for international trade must be fumigated or heat-treated, explains Kerry Britton, a national pathologist with the U.S. Forest Service who studies invasive forest pests.

Another strategy: Britton notes that researchers are trying to breed ash trees with natural resistance to EAB by crossing Asian ash trees that fight off the pest with vulnerable North American ash species.

“By the time the beetle was detected, it could not be eradicated,” Britton says. “The goal now is to slow it down.”

One Green Thing You Can Do:

Don’t move firewood from quarantined areas. One study showed that EAB can establish on a credit card-size piece of bark.

Keep an eye out for EAB, whether in your yard or your neighborhood. Here’s a helpful guide to identifying ash trees and distinguishing between EAB and other problems. Realistically, your best bet is to call an accredited tree care company since early evidence of EAB damage occurs at the treetop level, where it’s not visible to most folks. Now is the time to act. Treating trees by mid-May minimizes the damage by adult beetles, which emerge in the spring. If detected early, trees can be treated with insecticide rather than being cut down. 

Think you spotted one? Report it to your state’s agriculture department office or the call USDA’s EAB toll-free hotline at 1-866-322-4512.


The unofficial EAB web site with background and treatment information, a collaborative education effort by state universities and the U.S. Department of Agriculture Forest Service

A map showing EAB detections across the U.S. and Canada as of December, 2012 (does not reflect the recent discovery of EAB in New Hampshire)

To save or not to save? A guide deciding when to treat EAB

Summary argument by Coalition for Urban Ash Tree Conservation on why ash tree conservation is preferable to wholesale tree removal

SLAM (Slow Ash Mortality) is a pilot project in Michigan – ground zero for EAB – to slow down beetle infestation.