What Does Emerald Ash Borer Infestation Look Like in Nebraska Trees?

What the Emerald Ash Borer is and why Nebraska should care

The emerald ash borer (Agrilus planipennis), commonly abbreviated EAB, is a small metallic-green beetle native to Asia that has become one of North America’s most destructive invasive forest pests. Since its detection in the United States in 2002, EAB has killed tens of millions of ash trees (Fraxinus species) across the country. Nebraska contains substantial populations of green, white, and black ash in windbreaks, riparian corridors, urban streetscapes, and natural woodlands. The arrival and spread of EAB in and around Nebraska threaten public safety, property values, biodiversity, and municipal budgets for tree removal.
Understanding what EAB infestation looks like in Nebraska trees is essential for early detection, timely treatment, and minimizing loss. Below are detailed, practical descriptions of symptoms, diagnostic clues, timelines, monitoring strategies, and management options tailored to Nebraska conditions.

Typical victim trees in Nebraska

Ash is the target genus for EAB. In Nebraska, the most commonly affected species include:

green ash (Fraxinus pennsylvanica)
white ash (Fraxinus americana)
black ash (Fraxinus nigra), where present in wet sites

These species are widely used in windbreaks, street plantings, and shelterbelts because they are hardy and fast-growing. Their prevalence makes EAB particularly damaging in Nebraska landscapes.

Early signs to watch for (first 1-3 years of infestation)

Early detection is difficult because the larval stage feeds beneath the bark and external symptoms can be subtle for one to several years. However, the following cues often appear first and should raise concern:

Decline in canopy vigor: individual branches producing fewer leaves, smaller leaves, or leaves that yellow earlier than neighboring trees.
Thinning crown: upper crown and branch tips exhibit sparse foliage compared with healthy ash trees nearby.
Vertical bark splits or loose bark: sometimes caused by larval galleries disrupting phloem and cambium tissues.
Woodpecker activity: increased woodpecker or flicker pecking (peeling bark) as they feed on larvae; often visible as patches of missing bark or shredded bark chips on the trunk.
D-shaped exit holes on the trunk and major branches: small (about 3-4 mm) and distinctive, but may not be abundant early on.

If you see one or more of these signs on ash trees in Nebraska, inspect more closely or contact local extension or forestry staff for confirmation.

Established infestation signs (3-5+ years)

When emerald ash borer infestation becomes well-established, symptoms intensify and become easier to identify:

Extensive crown dieback: progressive loss of branches from the top down. Within 3-5 years a heavily infested tree can be more than 50 percent dead in the crown.
Epicormic sprouting: clusters of water sprouts on the trunk or at the base of the tree as it attempts to compensate for canopy loss. These sprouts are a stress signal rather than a recovery sign.
Increased woodpecker damage and bark loss: large blocks of missing bark revealing S-shaped larval galleries underneath.
Abundant D-shaped holes and frass: many exit holes and sawdust-like bore dust (frass) accumulating in bark crevices, branch crotches, and at the base of the tree.
Rapid mortality in previously healthy trees: in cases of high infestation density or in smaller trees, death can occur within 3-5 years after first detection.

Diagnostic details: bark, galleries, exit holes, and frass

Bark and larval galleries
Under the bark, third-instar EAB larvae create serpentine, S-shaped galleries in the phloem and outer sapwood. These galleries disrupt the tree’s ability to transport water and nutrients, causing branch dieback and eventual death. If bark is peeled back on suspect trees, you will see:

Light-colored, winding tunnels with a distinct meandering pattern.
Galleries that may be packed with frass or appear clean depending on larval stage.
Galleries concentrated in the outer 1/4 to 1/8 inch of wood, often near branch crotches and major scaffold limbs.

D-shaped exit holes and frass

Exit holes: Adult beetles chew exit holes when emerging in late spring to summer. The holes are flattened on one side, creating the characteristic D-shape about the size of a grain of rice (roughly 3-4 mm across).
Frass: Larval feeding produces coarse, granular, wood-colored frass that may accumulate in bark crevices, under branch crotches, or in burlap and traps. In contrast to powdery dust produced by other borers, EAB frass is often fibrous and coarse.

Canopy symptoms and epicormic shoots

Crown thinning and dieback patterns

Pattern: Dieback typically begins in the upper canopy and progresses downward. A single branch here and there may die first, then entire tops of trees decline.
Leaf symptoms: Leaves may be smaller, sparser, and yellowing compared to healthy ash trees of the same age and environment.

Epicormic shoots and basal sprouts

Water sprouts: Heavy infestations provoke sprouting along the trunk or at the base. These shoots are often numerous, weakly attached, and a sign of severe stress rather than recovery.

How to differentiate EAB damage from other stressors

Several insects and diseases can cause ash decline in Nebraska, including ash yellows, root rot, storm damage, drought, and other borers. Key distinguishing features of EAB include:

Presence of D-shaped exit holes is diagnostic of EAB adults.
S-shaped larval galleries under the bark are distinct from the straight or branching galleries of other borers.
Rapid top-down thinning over a few years, combined with exit holes and woodpecker activity, points strongly to EAB.
Widespread mortality across multiple nearby ash trees (especially younger ones) suggests EAB rather than localized root issues or drought.

If in doubt, collect clear photos of the canopy, trunk, exit holes, and any galleries and contact county extension, state forestry, or certified arborist for confirmation.

Monitoring and early detection strategies for Nebraska landowners

Early detection increases the effectiveness of treatment. Recommended monitoring practices:

Inspect ash trees once or twice per year during late spring through summer for new D-shaped holes, increased woodpecker activity, and crown thinning.
Watch high-risk trees: street trees, shelterbelt specimens, and ash in proximity to known EAB infestations or to firewood moved from infested areas.
Use traps and surveys: municipal forestry programs and extension offices may deploy purple prism traps or bark sampling; private landowners should coordinate with local authorities.
Document and map: keep simple records (photo, date, GPS or address) of suspected trees and any management actions taken.

Management options: treatment, removal, and costs

Once EAB is confirmed or suspected, options depend on tree value, infestation stage, and budget.
Preventive and curative insecticides

Systemic trunk injections and soil-applied systemic insecticides (neonicotinoids and emamectin benzoate) are effective when applied according to label directions. Emamectin benzoate is currently one of the most effective treatments for protecting and saving moderately infested trees for several years.
Timing and professional application: Treatments are most effective when applied before heavy infestations and should be administered by certified applicators. Repeat treatments may be necessary every 1-3 years depending on product and pressure.

Removal and replacement

Heavily infested trees that are hazardous or near death should be removed promptly to eliminate safety risks from falling branches and to reduce local beetle populations.
Disposal: Do not move ash firewood from infested to uninfested areas. Follow state quarantine or disposal guidance.
Replacement: Replant with diverse, non-ash species to reduce future pest risk and restore canopy coverage–consider native species adapted to Nebraska soils and climate.

Cost considerations

Treatment costs vary with tree size, product, and applicator rates; removal and stump grinding increase total costs. Municipal budgets must account for removal of hazard trees along streets and in parks. Proactive treatments on high-value trees can be less expensive long-term than removal and replacement in urban settings.

Legal, reporting, and community coordination in Nebraska

If you suspect EAB in Nebraska, report observations to your county extension office, the Nebraska Forest Service, or other state forestry agencies. Many states maintain reporting hotlines and mapping programs to track spread and coordinate quarantine measures. Community coordination helps with early detection, targeted treatments, and funding for removals and replacement plantings.

Practical takeaways for homeowners, landowners, and managers

Learn to recognize the signature signs: D-shaped exit holes, S-shaped galleries under bark, canopy thinning from the top down, and epicormic sprouting.
Inspect ash trees annually during late spring and summer, and take photos of any suspicious symptoms.
If you find D-shaped holes or heavy woodpecker damage, consult University Extension, a certified arborist, or the Nebraska Forest Service for confirmation and recommendations.
For high-value or shade-providing trees, consider prompt preventive or curative insecticide treatments administered by professionals. For trees that are heavily infested, prioritize safe removal.
Do not move ash firewood. Use local wood or properly debark and heat-treat wood according to state guidelines to limit spread.
Plan for long-term diversity: when replacing trees removed for EAB, plant a mix of species suited to Nebraska conditions to prevent future single-pest vulnerabilities.

Final note: vigilance pays off

Emerald ash borer is a lethal pest, but timely detection and coordinated action can save valued trees and slow spread. Nebraska landowners and managers who become familiar with the characteristic visual and physical signs, inspect annually, and act early will have the best chance to retain ash trees that are worth saving and to manage the landscape cost-effectively as EAB presence increases.