Emerald Ash Borer Diagnostic Guide

Agrilus planipennis

The Emerald Ash Borer (EAB) has killed millions of ash trees since its discovery in southeastern Michigan in 2002. Native to Asia, this insect was probably introduced to the United States in wood packing material carried in on cargo ships or airplanes. Through a combination of natural spread and human activity it is now found in the northern portion of the Midwest and east coast. Minnesota to Maine to Georgia. Colorado and Kansas also contain EAB. All of these locations place millions of additional ash trees at risk. It will continue to spread.

Trees at Risk

All native ash trees, including green, white, black, blue, and pumpkin ash.

Green Ash

Signs of Damage


D-Shaped exit hole

Symptoms of an early infestation may be difficult to diagnose. Be on the lookout for multiple declining ash in a given area and D-shaped exit holes that are approximately 1/8 “ in diameter. As an infestation progresses, small vertical splits in the bark can be seen on twigs or the main trunk and woodpecker holes may be present on trees. Trees may die after 2-4 years or less.

Thinning canopies are symptoms of EAB

 Physical Appearance


Adult EAB

  • Typically the top 1/3 of crown shows dieback and thins. Trees appear to lose about 30%-50% of their canopy after 2 years of infestation.
  • As the tree declines, epicormic shoots form at the interface between healthy and dead tissue anywhere in the canopy.
  • Distinct “S” shaped, frass-filled larval galleries that can range from 4- 20“ in length etch the xylem and phloem.
  • Adults are slender and can be 1/4” to 1/2” in length, they are dark metallic emerald green.
  • Larvae range in size from 1 -1 1/4” in length with pincer-like appendages on the last segment

Larval galleries under the bark

How Does Emerald Ash Borer Kill a Tree?

As the larvae develop inside the tree, they consume the vascular tissue of the tree. During this process, they weave back and forth creating “S” shaped galleries in the vascular tissue. These “S” shaped galleries essentially suffocate the tree, cutting off vital fluids to the canopy. This activity occurs behind the bark and can go unseen for years before signs or symptoms appear on the tree


Often times, when symptoms begin to appear on the tree, the tree has already been infested for multiple years. Additionally, it is rare to see an adult borer which makes identifying infested ash trees even more difficult. Prevention with insecticide products is critical when it comes to protecting ash trees from emerald ash borer.



Emerald ash borer is a non-native borer that attacks all North American species of ash to varying degrees. Accidentally introduced into southeastern Michigan, it was first detected in 2002 and since has killed millions of ash trees in forests and urban environments.

Emerald Ash Borer Life Cycle

  • Emerald ash borer pupate in early spring and emerge as adults in mid-May and June.
  • They lay their eggs in the bark crevices on ash trees in mid-July.
  • The eggs hatch and the EAB larvae will then bore into the tree and feed in the tree’s vascular tissue.
  • The larvae will overwinter in the tree and emerge in the spring as adults, starting the cycle all over again.

Treatment Strategy

The best protection from EAB is prevention. Treat all species of ash within a 15 mile radius of nearest known infestation. Infested ash trees displaying <50% dieback can be saved. However, treatments applied to ash trees in early stages of dieback will provide a higher likelihood for success. Emamectin benzoate has performed well on infested trees.

EAB At Risk Trees

Emamectin benzoate by Tree Injection is also an option and is effective for 2 years.

  • Tree Injection using Arbormectin

    Dosage: Refer to label
    Timing: Growing season
    Re-Treatment: Every 2 years
    Arbormectin Login for pricing
  • Soil Application using Xytect 2F

    Dosage: 6 mL/in DBH for trees <15 in, 12 mL/in DBH for trees> 15 in DBH
    Timing: Spring or fall
    Re-Treatment: Annually
    Xytect 2F Insecticide
    Xytect 2F Login for pricing
  • Soil Application using Xytect 75WSP 22 packets

    Dosage: 1 pkt treats 24 in DBH for trees less than 15 in DBH, 1 pkt treats 12 in for trees greater than 15 in DBH
    Timing: Spring or fall
    Re-Treatment: Annually
    Xytect 75WSP 22 packets
    Xytect 75WSP 22 packets Login for pricing
  • Soil Application using Transtect

    Dosage: 1 pkt for each 5 in of DBH
    Timing: Spring or early to mid-summer
    Re-Treatment: Annually
    Transtect 70WSP Insecticide
    Transtect Login for pricing
  • Systemic Bark Spray using Transtect

    Dosage: 6-12 packets in 1 gal of water. When using bark spray, apply 2 oz mixed solution/in DBH
    Timing: Spring or early to mid-summer
    Re-Treatment: Annually
    Transtect 70WSP Insecticide
    Transtect Login for pricing

Treatment Expectations

  • Preventive treatments will provide greater likelihood for success than treatments on infested trees.
  • Recognize that it is difficult to detect the presence of EAB during the early stages of infestation, thus ash trees may be protected from EAB by applying treatments prior to the onset of visible symptoms.
  • When symptoms are present, the tree has been infested for several years and the chance of saving it decreases. Trees with up to 50% symptoms have been saved. However, treating infested trees carries a higher risk of failure.
  • Continuous treatments are required for continued protection. If applications cease, trees will become susceptible to the pest.
  • Xytect™ 75 WSP and Xytect™ 2F may take 30-60 days or more to be taken up into the tree to protect the tree from EAB attack.
  • Transtect™ soil and systemic basal bark sprays will provide faster protection (30 days or less) than Xytect™ soil applications.
  • Research at Ohio State has demonstrated that at least 8, but up to 12 packets per gallon is effective on trees up to 25 inches. Use the higher rate for larger trees, and trees that are under higher EAB pressure.

EAB Treated Untreated

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy Use of the images does not imply endorsement of treatments by

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