Updated June 25, 2024 . AmFam Team
Have you noticed something a little "off" about one of the trees in your yard? Perhaps the springtime foliage is more sparse than usual, or the leaves are a bit less vibrant. Maybe you've seen some strange holes that weren't there before, caused by little green insects or woodpeckers that are flocking to your neighborhood in unusually high numbers.
All of these could be signs of an emerald ash borer infestation affecting the trees on your property and in your community. Not to worry! We're here to help keep you informed about what you can do to treat your trees and keep your yard in tip-top shape.
The emerald ash borer (sometimes abbreviated as “EAB”) is an invasive insect originating from northeast Asia. Experts believe it first arrived in North America through a lumber shipment to the Detroit region sometime in the 1990s.
This wood-boring beetle feeds off soft, nutritious material beneath the bark of ash trees. While adult beetles typically cause only minor damage by nibbling on foliage, the most serious threat lies with the larvae — hungry offspring responsible for devouring away at the tender tissue of the ash tree.
Unfortunately, emerald ash borer spreads rapidly when people move firewood and other unprocessed timber. Today, emerald ash borers can be found in at least 33 states, from Maine to Texas, where they have the potential to impact 21 different species of ash tree.
Since the identification of the beetle in 2002 around the Detroit area, experts estimate the emerald ash borer has killed as many as 40 million ash trees in Michigan, with tens of millions additional trees destroyed elsewhere.
If you’re a homeowner with an ash tree on your property — especially if you’re in an affected region — you will want to be vigilant about this invasive pest. Losing ash trees to an emerald ash borer infestation could negatively affect your curb appeal and, as a result, your property value.
Even if you don’t have ash trees on your property, you may have them in your neighborhood. Ash trees are often used in landscaping due to their color, size and shade coverage, and today make up about 20% of the total tree population in urban and residential settings. In fact, ash trees are so prevalent in American cities that they have come to be known simply as “street trees.” Your neighborhood might look very bare without them!
Ash trees are economically important, too. Broadly speaking, ash trees are among some of the most valuable and abundant trees in the United States, with an estimated 7 to 9 billion ash trees in the country. The wood of ash trees is used for furniture, doors, flooring, architectural accents and several other home improvements. Fewer healthy ash trees could mean higher home improvement and building costs.
Many recreational hobbies use pieces of ash wood, too. Things like guitars, baseball bats, hockey sticks and oars — all of which can be costly enough as is.
The good news is that, in North America, emerald ash borers only attack true ash trees. That means your maples, oaks, willows and beech trees are all safe from this pest. In addition, mountain ash (which is not a true ash, but rather a type of rowan tree) is not known to be affected.
In the United States, most ash trees are located in the Midwest and Northeast. If you live in this part of the country, you may likely have an ash tree or two around your home or community. However, ash trees can be found nationwide, so it’s good to know what an ash tree looks like in comparison to your other trees.
Ash trees are best identified by focusing on three key characteristics:
Next time you take a stroll through your yard or neighborhood, you may come across these invasive little beetles. Knowing what to look out for — and when — could mean saving you the cost and effort of tree removal. When inspecting trees for adult emerald ash borers, keep an eye out for metallic green insects about a half-inch long — a little smaller than a dime. The insect is fairly long and skinny, not round like some other beetles. When it opens its wings and carapace, you can see its uniquely copper-red abdominal segments.
Unfortunately, adult emerald ash borers may not emerge until after the infestation is well underway and serious damage has already been done to your tree. To catch problems early, you’ll need to know when to look for the different phases of the emerald ash borer life cycle.
Most emerald ash borer infestations start in the summer months.
Starting in May, adult emerald ash borers will emerge from infected trees. They leave distinct, D-shaped holes in the tree’s bark. After mating, females will start looking for ash trees where they can lay their eggs. Most of these beetles will travel less than 1/2 mile from their original location unless transported in firewood or other unprocessed wood products. If you spot adult emerald ash borers in late May or early June, that’s a sure sign that an infested tree is nearby.
In June through September, emerald ash borers will lay 40-200 eggs in crevices in the bark of ash trees. The round, reddish-brown eggs are incredibly small — only about 1 millimeter in diameter — and nearly impossible to find. The eggs hatch after about two weeks.
From June to October, the insatiable larvae will feast on the soft wood just under the bark. An emerald ash borer larva is creamy white in color and looks a bit like a worm, with a flat head and bell-shaped body segments. They often form S-shaped patterns under the bark called galleries. At maturity, they can be up to 1.5 inches long. The larvae will live and feast under the bark for up to two years and conduct the most destructive phase of an emerald ash borer infestation.
In September or October, when temperatures start to cool, mature larvae will overwinter in the tree’s sapwood. Here they will pupate and transform into adults. The emerald ash borer pupa is looks like a creamy white, segmented cocoon. Then in late spring and early summer of the following year, the adult emerald ash borers emerge, starting the life cycle all over again.
To check an ash tree for larval infestation, carve away a small portion of the trunk’s bark and underlying sapwood. Look for S-shaped tunnels and whitish, worm-like larvae.
Eggs, larvae and pupae can all survive in firewood if it is transported — even if it is stored over the winter — so you should be careful about transporting firewood all year round.
An emerald ash borer infestation can kill a young ash tree in as little as a year if left untreated, so early detection is crucial. Thankfully, with a little awareness and education, early detection can be as easy as looking out of your window.
Healthy ash trees should have dense green foliage, without any bare or sparse branches. Branches should bend, rather than break, and there should be an absence of dead or broken branches.
Early signs of emerald ash borer damage are most visible at the top of the tree, called the crown or canopy. The first sign is often yellowing or browning leaves at the very top of the tree, followed by leaf die-back that results in branches with few or no leaves. Be sure to stand far back from your ash tree when inspecting the crown, as it can be nearly impossible to tell if there has been thinning or leaf die-back if you are standing too close. Up close, you may notice small notches in leaves where adult emerald ash borers have been feeding.
A sudden increase in woodpecker activity can also be a sign of infestation. Woodpeckers are known to dine on emerald ash borer larvae, so if you’re rudely woken by a number of woodpeckers pecking at your tree one morning, there could be a good chance they’re trying to score an emerald ash borer breakfast. Sometimes enthusiastic woodpeckers can even cause something called “blonding,” where the tree trunk appears paler because the hungry birds have stripped away so much of the outer bark.
During the summer, you can cut away a small portion of a tree’s bark and sapwood. A telltale sign of infestation are the unique serpentine tunnels or galleries created by the feeding larvae. You may even spot larvae in these galleries!
Later signs of infestation include a dull, sickly crown where the leaves are no longer vibrant, healthy or plentiful. You may also find tiny, D-shaped holes where adult beetles have emerged. Other signs of advanced infestations include splitting gashes in the trunk from calluses formed below the bark after substantial internal ash borer damage, or strange foliage sprouting from the trunk or roots with larger-than-normal leaves.
Key signs of emerald ash borer disease:
Yellow, thinning or wilting leaves
S-shaped tunnels under the bark
Peeling bark
Defoliation of leaves
D-shaped holes in the bark
Unusual woodpecker activity
Strange growth at trunk or roots
Upright shoot growth
The first step to action is taking an inventory of your ash trees. Determine how many ash trees you have, where they are and whether you want to treat the infestation or remove the affected trees. If trees are left untreated, they are unlikely to recover and can die within a handful of years.
Next, you’ll want to consult the aid of an arborist or tree care professional. Arborists are certified tree specialists who could be thought of as “tree doctors.” They can verify that emerald ash borers — and not a different pest — are infesting your trees, and help you decide whether emerald ash borer treatment or removal of the affected trees is the best option for you, your yard and your wallet. They can also help you determine if it’s a good idea to apply a preventative emerald ash borer treatment to any ash trees in your yard not yet infested.
If you decide not to treat or remove an infested tree, an arborist will also be able to assess the situation and make helpful recommendations that could prevent hazards and damage to your, or your neighbor’s property, if the afflicted tree dies.
Deciding whether to treat or remove an infested tree is a tough choice that expert Wayne Rayfield knows all too well. A landscape professional with over 30 years of experience, including over 20 years as a college instructor for landscape design, he now works as a land management administrator who helps maintain American Family Insurance’s 450-acre National Headquarters. Over the years, he’s had to deal with several emerald ash borer infestations.
When making the tough decision to keep or replace an ash tree, Wayne advises homeowners to consider four factors: the tree’s sentimental value, its size and health, its location on the property and the cost of emerald ash borer treatment.
First some sentimental value. “If you have a real stately tree that’s got the kids swing on it for generations and you’re catching it early, there’s value in that,” Wayne explains. Younger trees that haven’t established the same sentimentality to the homeowner may be easier to replace with a more reliable, durable species that, Wayne says, “won’t take long to catch up to the other young tree.”
Next is the size and health of the tree. “When you’re dealing with a large, real specimen tree, the cost to remove it is thousands. But to replace it, you never could. If you have, say, thirty years of growth, you can’t get that back.” In particular, mature trees with a diameter greater than 12 inches are particularly valuable — and may be impossible to replace.
Third is the location on the property. Trees planted in ideal landscaping locations, such as a mature tree that perfectly shades your deck, add much more value to your property than trees in less strategic locations.
Last is cost. Treating ash trees can be costly, and emerald ash borer treatment isn’t always successful. In Wayne’s experience, “if you’re able to treat the tree, you’re looking at around $200 to $500 every two to three years” for professional treatments.
There are also DIY treatment options, such as insecticides, but the regulations differ between states. Before attempting any DIY treatments, you should contact your state’s department of agriculture (or equivalent agency) for further guidance. You may also want to check in with your county or city to see if there are additional local regulations, resources or recommendations.
In sum, Wayne suggests considering ash borer treatment for more mature trees, at a diameter greater than 12 inches, and trees planted in ideal landscaping locations. For younger trees, crowded trees or trees in less-than-ideal locations, “then you have to really think, is it something you want to invest in over the life of the tree?”
Depending on the overall health of the tree, along with its location and value to you, you may just opt to remove or replace the tree altogether, choosing instead a species of tree much less susceptible to infestation — such as maple, honey locust or gingko trees — while providing the same utility and landscaping benefit.
Depending on the size and the location of the tree, tree removal costs could range anywhere from $100 to $1,500 or more to have it removed professionally. Remember, professional removal is the only safe way to remove a tree. Attempting to remove a tree yourself can be extremely dangerous — to you, your home and your neighbors’ property.
Unfortunately, tree removal is sometimes the only option, as emerald ash borer infestations are often more severe than homeowners realize. Wayne even recalled one heartbreaking situation where a nursery had to bulldoze hundreds of acres of ash trees potentially infested by the beetle.
According to Wayne, “The bottom line is, if you see any kind of activity, you’re pretty deep into it and it may be difficult to recover. The best plan would be to begin treating your tree before the bore gets into it.”
The good news is you can take action before you see any signs of emerald ash borers in your yard or neighborhood. Preventative ash tree borer treatments are available that can keep emerald ash borers out of your ash trees.
“If you have a nicely placed ash tree and it’s a good size — they say 12” in diameter — and you can treat it before it gets the borer, there can be value in that,” explains Wayne. “A nicely landscaped property, with trees in the right places, will increase your property value.”
The most effective method of ash borer beetle prevention begins with a consultation with a tree expert. This is especially true when you have a larger tree — a tree greater than 45 inches in circumference — which you will likely need injections administered by an arborist.
If that isn’t an option, or you would like to treat a small (less than 45 inches in circumference) tree the DIY way, you would need to visit a garden center to evaluate various insecticidal options. It’s always a good idea to speak to a specialist regarding consumer-grade emerald ash borer treatment. The best time to treat ash is during the springtime, between April and May.
You can also help your community fight emerald ash borer. If you spot signs of the pests’ activity in your own yard or in your neighborhood, be sure to alert your neighbors. While municipal agencies generally do not handle privately owned trees, you should contact your city’s streets department if you spot a city-owned treat affected by emerald ash borer.
Most homeowners insurance does not cover the treatment or removal of trees infested by emerald ash borer or any other pest, fungus or disease.
However, if you have a tree that has been weakened or killed by the pest, and the tree falls due to covered peril such as a storm, fire or vehicle collision with the tree, your homeowners insurance may cover the resulting ash borer damage. Depending on your specific policy and coverages, your insurance may help pay for the cost of removing the fallen tree, repairing any property it has damaged (such as your home or garage, or any of your neighbor’s structures that were impacted) and any injuries caused by the falling tree.
However, it’s always best to be proactive. Don’t wait until a dead or dying treat has harmed your home or your loved ones! If you have a tree in concerning condition, get in contact with a local expert. Remember, you can always check in with your American Family Insurance agent for recommendations for contractors or if you have questions about your policy.
This article is for informational purposes only and based on information that is widely available. We believe this information is accurate but do not make any guarantees or promise any results based on this information.
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