Frequently Asked Questions on the Emerald Ash Borer

FAQ From Wisconsin Homeowners About The Emerald Ash Borer

By now, just about everyone has heard about the Emerald Ash Borer (Agrilus planipennis). We still get numerous questions about this pest, though, so we have compiled some of the most frequently asked questions about the Emerald Ash Borer (aka EAB) into this blog post.

As we enter into spring, it’s extremely important to know that mid-April to Mid-May is the best time of year to apply a preventive pesticide treatment to any ash trees you have on your property. You do not need to have an EAB infestation to apply this pesticide.

Preventive treatment of an ash tree is simple enough for most homeowners to do on their own, but we can also do this for you. To be fully effective, treatment must be performed annually. Handling an active infestation sometimes requires more aggressive treatment methods, such as injections into the trunk of the tree.

If you prefer, we can handle both preventive treatment of your ash trees and the treatment of any ash trees which have already been infested—provided it is not too late to try to salvage the tree.

Which ash trees are prone to Emerald Ash Borer infestation?

All of them-- green, black, white and blue ash trees can all fall victim to the EAB. The only ash not vulnerable is the mountain ash, which despite its name isn't actually an ash species.

What is the Emerald Ash Borer and how did it get here?

The emerald ash borer is a small (about 1cm long), wood boring beetle with a metallic emerald-green coloration. The insect is native to Asia, and the best guess of experts is that it inadvertently got into the US while burrowed into the wood of shipping crates from China.

How does the Emerald Ash Borer harm trees?

In its larval stage, it kills ash trees by eating away at the tree’s soft sapwood underneath the bark.  This interferes with the tree’s ability to distribute water and nutrients between its roots and the rest of the tree, which results in the tree starving to death. The first part of the tree to die is the canopy.

The life cycle of an emerald ash borer is about one year, most of which is spent as a voracious larva. Adult insects emerge from the tree in early summer and live for about 3 weeks, during which they mostly feed on ash leaves and lay eggs in crevices of the bark on ash trees. Their leaf chewing does little harm, but the egg laying ensures another generation of insects will put the tree at risk. Within 2 to 4 years of infestation, most ash trees die.

Doesn’t the Emerald Ash Borer die over the winter?

Unfortunately, this doesn’t seem to be the case. The winter of 2014 was one of the coldest the Midwest ever endured. So cold that over 90% of the surface area of the Great Lakes was frozen solid. Still, the Emerald Ash borer survived. In fact, a study of ash trees in Michigan didn’t turn up a single dead larva. They burrow deep into the trunks of trees, where they are apparently insulated from the cold. Then, come spring, they emerge as beetles to mate and lay more eggs.

How long does it take the Emerald Ash Borer to kill a tree?

It might surprise you to learn this, but these voracious insects can destroy a tree in as little as two years. This is why it’s important to recognize the signs of an infestation early and to contact a Certified Arborist as soon as possible.

Are ash trees the only trees at risk?

The good news is that, thus far at least, the insect has only been found in ash trees. The bad news: these pests have already destroyed millions of ash trees across 26 states and even in Windsor, Ontario. Besides wiping out the arboreal gems of many neighborhoods, the insect has also wreaked havoc on the lumber industry.

How serious is the problem?

In a word: Very.

The insect was first discovered in the summer of 2002 in southeastern Michigan, near Detroit. From there, it has spread rapidly across the Midwest, the south and even into Ontario. Although the insect can fly no more than a few miles, unsuspecting people transporting firewood and plants across state lines have accelerated the spread of the emerald ash borer.

At last check, the insect has been found in Ohio, Indiana, Illinois, Maryland, Pennsylvania, Virginia, West Virginia, Missouri, Minnesota, New York, Kentucky, Iowa, Tennessee, Connecticut, Kansas, Massachusetts, New Hampshire, North Carolina, Georgia, Colorado, New Jersey, Arkansas and Louisiana.

To give you an idea of just how serious the threat is, Andrew Liebhold, a research entomologist with the United States Forest Service, is on record as stating: “Ninety-nine percent of the ashes in North America are probably going to die.” Professor Deborah McCullough of Michigan State, has a slightly less dire prediction. She predicts that although the black ash and green ash variants of the species are probably doomed, the emerald ash borer “only” kills 60 to 70 percent of the blue ash species. The fate of the white ash, the fourth type of ash, is somewhere in between total annihilation and about a 15% chance of survival.

What are the signs of Emerald Ash Borer infestation?

Because most of the damage being done by the beetles is inside the tree, it's easy to miss some of the telltale signs of an infestation if you don't know what to look for. If you have any ash trees in your yard and notice anything not quite right with them, it's worth getting a certified arborist to take a look. 

Usually, the first thing most homeowners notice is the canopy of their ash tree turning brown and thinning out. If more than half of the canopy is gone, it’s probably too late to try saving the tree. Some experts go even further, contending that if a tree shows more than a 20% loss of its canopy, treatment probably won't have any effect.

However, there are other signs to look for which may help you spot an infestation well before the tree canopy starts dying:

  • D-shaped exit holes in the bark (about 1/8” in size) from where adult emerald ash borers exit the tree
  • Vertically splitting bark
  • More woodpeckers than usual feeding on the tree
  • Low sprouting shoots from the main trunk (known as epicormal growth). This is a sign of stress often related to EAB infestation.
  • Leaves changing colors earlier than usual in fall
  • A less full canopy of leaves

If you suspect you may have an emerald ash borer infestation, we will be happy to send one of our certified Milwaukee arborists out to take a look and let you know if your tree is at risk or not. We can also provide you a free estimate for treating your tree.

What is the treatment for Emerald Ash Borer?

Treatment is twofold: In the spring, an insecticide put down on the soil around the tree is absorbed through the tree's roots. This approach has been found to be 80% successful. At other times of the year, we inject insecticide into the tree trunk. This has been shown to be about 95% successful. The key to any successful treatment, though, is treating the tree before the damage is too extensive.

Our recommendation: If you have any ash trees on your property and don't want to risk losing them to the emerald ash borer, have one of our certified arborists come out once a year to inspect it. We'll be able to spot any early signs of EAB infestation--when it's still possible to save a tree.


Contact our Milwaukee certified arborists online to request a free tree care estimate.