Emerald Ash Borer: How to Identify and Treat It

An ash tree that once provided shade and greenery can begin to look unhealthy without an obvious explanation. Its leaves may thin, branches may die back, or unusual marks may appear on the trunk. One possible cause is Emerald Ash Borer (EAB), an invasive beetle that threatens ash trees across Minnesota.

Recognizing an emerald ash borer infestation early can help homeowners understand their options before the tree becomes severely damaged. Depending on the tree's condition, treatment may help protect it, while removal may be necessary if it becomes structurally unsafe.

In this guide, we'll explain how to identify Emerald Ash Borer, recognize common symptoms, understand treatment options, and determine when to contact a professional tree care service.

What Is Emerald Ash Borer?

Emerald Ash Borer (Agrilus planipennis) is an invasive, wood-boring beetle native to Asia. It was first identified in Minnesota in 2009 and has become a serious threat to the state's ash trees.

The adult beetle is small and metallic green, but much of the damage happens beneath the bark.

EAB larvae feed on the inner bark and create winding tunnels through the tree's tissues. As these galleries accumulate, they interfere with the movement of water and nutrients between the roots and the canopy. The tree gradually loses vigor, branches begin to die, and an untreated infestation can eventually kill it.

How Does Emerald Ash Borer Damage Ash Trees?

The damage often develops gradually, making an early infestation difficult to recognize.

As larvae feed beneath the bark, they create galleries that disrupt the tree's ability to transport essential resources. Over time, this can lead to:

• Thinning foliage and a declining canopy

• Dead branches, particularly near the top

• Vertical bark splits

• New shoots growing from the trunk or lower branches

• Progressive decline in tree health

  
  

Ash trees that are severely affected may eventually become hazardous, particularly when dead branches or weakened sections are close to homes, driveways, and walkways.

Which Trees Are at Risk?

Emerald Ash Borer attacks ash trees belonging to the Fraxinus genus. Common North American ash species affected by the pest include green ash, white ash, and black ash.

Not every tree with similar-looking leaves or bark is an ash tree. For example, mountain ash belongs to a different genus and is not a host for EAB.

If you're unsure whether a tree on your property is an ash, confirm its identity before deciding on treatment.

How to Identify Emerald Ash Borer

Recognizing Emerald Ash Borer involves looking for the insect itself and the characteristic damage it leaves behind.

What Does an Emerald Ash Borer Look Like?

Adult Emerald Ash Borers are slender, metallic-green beetles approximately 3/8 to 1/2 inch long. Their small size and green coloring can make them difficult to distinguish from other insects.

Finding a green beetle alone does not confirm an infestation. Identification is more reliable when the insect is associated with an ash tree and other characteristic signs are present.

Look for D-Shaped Exit Holes

One recognizable sign is a small, D-shaped exit hole in the bark. These openings are created when adult beetles emerge from the tree.

The holes are approximately 1/8 inch wide and may be difficult to spot, especially when they occur high on the trunk or branches.

Check for S-Shaped Galleries

EAB larvae create winding, S-shaped galleries beneath the bark as they feed. These tunnels are a strong indicator of Emerald Ash Borer when found in an ash tree.

However, examining galleries generally requires access beneath the bark. Avoid damaging a tree simply to investigate a suspected infestation. A qualified professional can help determine whether further inspection is appropriate.

7 Common Signs and Symptoms of Emerald Ash Borer Infestation

An emerald ash borer infestation may not be obvious in its early stages. As damage progresses, several warning signs can appear.

1. Thinning Canopy

One of the first visible changes may be a reduction in the tree's usual leaf density. The canopy may look sparse, with fewer leaves or smaller leaves than expected.

2. Crown Dieback

Branches near the top of the tree may begin dying before the lower canopy shows extensive damage. As the infestation progresses, dead branches can become more widespread.

3. Woodpecker Flecking

Woodpeckers feed on larvae beneath the bark. Their activity can leave lighter patches on the trunk where sections of outer bark have been removed.

This can be an important clue, although woodpecker damage alone does not confirm EAB.

4. D-Shaped Exit Holes

Small, D-shaped holes in the bark are a characteristic sign of adult Emerald Ash Borer emergence. Because they may be difficult to see, their absence does not rule out an infestation.

5. S-Shaped Larval Galleries

Winding galleries beneath the bark indicate larval feeding. When these characteristic tunnels are found in an ash tree, they provide strong evidence of EAB activity.

6. New Shoots Growing From the Trunk

An affected ash tree may produce new shoots from its trunk or lower branches. These are sometimes called epicormic sprouts and can appear as the tree responds to stress.

7. Vertical Bark Splits and Declining Health

Vertical cracks or splits in the bark can occur as the tree responds to damage beneath the surface. Other causes are possible, so this symptom should be considered alongside the tree's overall condition.

These emerald ash borer signs do not all appear at the same time. Other problems, including drought, root damage, and different wood-boring insects, can cause similar symptoms. If you notice several warning signs of damage, arrange a professional inspection rather than assuming the cause.

How Does Emerald Ash Borer Treatment Work?

The right emerald ash borer treatment depends on the tree's health, the level of infestation risk, and the amount of damage already present.

Treatment is generally most useful for ash trees that retain most of their canopy and have not suffered extensive decline. Insecticides cannot reverse structural damage that has already occurred.

Can an Ash Tree Be Saved After an Infestation?

In some cases, yes.

A lightly infested ash tree may respond to appropriate insecticide treatment if it remains in reasonably good condition. A tree that has lost half or more of its canopy is generally a poor candidate because the damage may already be too extensive.

Before deciding on treatment, consider:

• How much of the canopy remains healthy

• Whether branches are dying or breaking

• The tree's structural condition

• The likelihood of EAB exposure in the area

• The cost of treatment compared with the tree's value and condition

  
  

A professional assessment can help determine whether protecting the tree is a reasonable option.

When Should You Consider Ash Tree Treatment?

It is better to evaluate treatment options before an ash tree becomes severely damaged.

Homeowners should consider the local EAB situation, the tree's condition, and whether the tree is worth protecting over the long term. The Minnesota Department of Agriculture maintains an Emerald Ash Borer information page, including resources for tracking the pest's distribution.

If EAB is present in your area, a tree care professional can help you evaluate whether preventive treatment or treatment of a suspected infestation makes sense.

Treatment or Removal: How Do You Decide?

Treatment and removal serve different purposes.

Treatment may help protect a healthy or lightly affected ash tree. Removal may be more appropriate when the tree has extensive canopy decline, significant structural damage, or hazardous dead branches.

The decision should account for both tree health and safety. A tree that is close to a home or frequently used area may require particular attention if its condition is deteriorating.

Emerald Ash Borer Treatment Options

There are several approaches to emerald ash borer control, but not every option is appropriate for every tree.

Systemic Insecticide for Ash Trees

Systemic insecticides are used to protect suitable ash trees by allowing the active ingredient to move within the tree.

Injecting an insecticide into the trunk is a professional option. The product used, application method, and interval between applications depend on the size and condition of the tree, risk of infestation, and product label.

University of Minnesota Extension identifies trunk injections using products containing active ingredients such as emamectin benzoate or azadirachtin as professional treatment options. Treatment commonly needs to be repeated at intervals determined by the product and conditions.

Professional Emerald Ash Borer Insecticide Treatment

A qualified professional can assess the tree and determine whether an insecticide treatment is appropriate.

Professional treatment can be particularly useful for larger ash trees, where application may require specialized equipment and knowledge of the correct product and timing.

Before proceeding, ask about :

• The recommended treatment and why it is suitable

• The product's approved uses and application requirements

• How often treatment must be repeated

• Potential environmental considerations

• The tree's expected response and limitations of treatment.

Pesticides should always be used according to their registered labels and applicable regulations. A treatment should not be presented as a guarantee that an ash tree will survive.

When Is Ash Tree Removal the Better Option?

Sometimes, removal is the more practical or safer decision.

An ash tree with extensive dieback or serious structural weakness may not benefit enough from treatment to justify the cost. Dead and declining ash trees can also become more difficult and hazardous to remove as branches become brittle and structural decay progresses.

Removal may be appropriate when:

• The tree has extensive canopy loss.

• Major branches are dead or breaking.

• The trunk has significant structural damage.

• The tree presents a risk to people or property.

• A professional determines that treatment is unlikely to help.

  
  

If removal is necessary, make sure the company understands the applicable Minnesota requirements for handling and transporting ash wood. EAB-related restrictions can affect how potentially infested material should be moved and disposed of.

How to Prevent Emerald Ash Borer Infestation

There is no way to guarantee that an ash tree will remain free of EAB, but monitoring and timely decisions can help protect suitable trees and limit the spread of the pest.

Monitor Your Ash Trees

Check for changes in the canopy, dead branches, woodpecker flecking, bark splits, and other unusual signs. Remember that symptoms may not appear immediately after an infestation begins.

Check Local EAB Activity

Use the Minnesota Department of Agriculture's EAB resources to review current information about the pest's distribution. Local risk can help inform whether preventive treatment is worth considering.

Discuss Preventive Treatment

Consider preventive insecticide treatment for good, healthy, valuable trees when the risk of EAB is high. Contact a certified arborist to help evaluate whether preventive insecticide treatment is necessary and to ensure proper maintenance procedures.

Avoid Moving Potentially Infested Firewood

Moving infested ash wood can help spread Emerald Ash Borer to new areas. Minnesota has restrictions on moving ash material and hardwood firewood, so check current state guidance before transporting wood.

Plan for Long-Term Tree Health

Regular inspections and appropriate maintenance can help identify other problems that may affect an ash tree's condition. Pruning dead branches and addressing tree health concerns can be useful, although these measures do not eliminate EAB.

When Should You Call a Professional for Ash Tree Treatment?

If you suspect Emerald Ash Borer, professional advice can help you avoid unnecessary treatment or removal.

Consider contacting tree care experts when:

• Your ash tree shows several EAB warning signs.

• The canopy is thinning, or the upper branches are dying.

• You are unsure whether the tree is an ash.

• You need to decide between treatment and removal.

• The tree is large or close to buildings, vehicles, or walkways.

• Dead branches or structural damage may create a safety concern.

  
  

If you are searching for Emerald Ash Borer treatment near me, check the provider's qualifications and confirm whether it offers the specific treatment you need. In Minnesota, the Department of Agriculture recommends using its Tree Care Registry when looking for tree care companies. Pesticide applications should be performed by appropriately qualified providers and follow applicable requirements.

Emerald Ash Borer and Ash Tree Care in the Twin Cities

Ash trees are an important part of Minnesota's urban and natural landscapes. For Twin Cities homeowners, monitoring their condition can help identify potential problems before an affected tree becomes severely damaged.

If an ash tree is declining, it is vital to verify if it is EAB or not before concluding that an infestation is present. Telling the difference between symptoms of other problems and EAB can make all the difference.

Depending on the state of the tree, the right treatment could be either a more detailed examination, treatment by a trained professional, pruning, or even the removal of the tree.

Primo Tree Experts serves homeowners across the Twin Cities metro area with tree removal, pruning and trimming, and other tree care services. If your ash tree has dead branches or appears to be declining, a professional assessment can help you understand the next steps.

Get Professional Help With Ash Tree Problems

Not sure whether your ash tree is showing signs of Emerald Ash Borer? Early assessment can help you understand the condition of the tree and whether treatment or removal should be considered.

Primo Tree Experts provides professional tree care services throughout the Twin Cities. If your ash tree is declining, has hazardous branches, or may need removal, contact our team to discuss your concerns.

Frequently Asked Questions

What Are the First Signs of Emerald Ash Borer?

Initial symptoms of attack may be exhibited by woodpecker activity, sparse foliage, and modifications to the tree's crown. You may notice semi-circle, D-shaped exit holes, or S-shaped galleries under the bark, but these can be tricky to spot. A combination of symptoms suggests you need to dig deeper.

Can an Ash Tree Recover From an Emerald Ash Borer Infestation?

Some lightly infested ash trees can recover or remain protected with appropriate insecticide treatment. Trees with extensive canopy loss or significant structural damage are less likely to benefit. A professional assessment can help determine whether treatment is worthwhile.

What Is the Most Effective Emerald Ash Borer Treatment?

Certain systemic insecticides, including professional trunk-injection treatments, can protect suitable ash trees. The appropriate product and method depend on the tree's condition, size, and infestation risk. No treatment can reverse structural damage that has already occurred.

When Is the Best Time to Treat Ash Trees for Emerald Ash Borer?

Timing is driven by the product, application method, and local circumstances. The University of Minnesota Extension considers May to late September as the window of opportunity for Minnesota ash trees with a full canopy and a receptive tree. Always consult the product label and professionals.

How Often Does Emerald Ash Borer Treatment Need to Be Repeated?

Treatment intervals vary by the active ingredient and product. Some professional trunk-injection treatments are repeated every two or three years, while other products may require different schedules. Ask the treatment provider for the recommended interval and ongoing cost.

Should I Remove an Ash Tree With Emerald Ash Borer?

Not always. A healthy or minimally stressed tree should be preserved, but a deteriorating or hazardous structural tree may have to be removed. If the tree is in a significant location and the cost of treatment cannot be justified, then removal is a consideration.

Can Emerald Ash Borer Spread to Other Trees?

Yes. Adult beetles can disperse on their own, and transporting infested ash wood or ash debris can establish the pest elsewhere. Follow updated Minnesota recommendations for disposal and transport of ash wood to prevent its spread.

How Do I Find Emerald Ash Borer Treatment Near Me?

Start by checking Minnesota's current EAB information and looking for a qualified tree care provider through the Minnesota Department of Agriculture's Tree Care Registry. Ask whether the provider offers EAB treatment, has the appropriate credentials, and can assess whether your tree is a suitable candidate.