Best Ways to Control Emerald Ash Borer in Wisconsin

Emerald ash borer (EAB) is an invasive beetle that has killed millions of ash trees across North America and remains a serious threat in Wisconsin. Managing EAB requires a mix of accurate identification, preventive actions, chemical and biological tools, and sound removal and replacement strategies. This article outlines practical, actionable steps for homeowners, municipalities, and arborists in Wisconsin, emphasizing timing, effectiveness, safety, and long-term planning.

Understanding the emerald ash borer

Emerald ash borer is a small metallic green beetle that attacks all species of ash (Fraxinus spp.). The larvae feed under the bark in S-shaped galleries, disrupting the tree’s ability to move water and nutrients, which causes crown dieback and eventual mortality.

Identification and signs to watch for

Early detection improves the chance to save trees. Common signs and symptoms include:

• D-shaped exit holes about 3 to 4 millimeters wide.
• Thinning or dieback that starts at the top of the tree and works downward.
• Vertical splits in bark and accumulation of S-shaped larval galleries under the bark.
• Increased woodpecker activity and bark flakes where woodpeckers feed on larvae.
• Epicormic shoots (sucker growth) on the trunk and main branches as the tree stresses.

Monitor trees annually, particularly mature ash greater than 2 inches diameter at breast height, and especially those in open sites or near known infestations.

Life cycle and timing in Wisconsin

Understanding the life cycle helps time treatments. EAB typically has one generation per year in Wisconsin. Adults emerge and fly from late May through July, with peak activity in June. Eggs are laid in bark crevices in early summer, and larvae feed under bark throughout the summer and overwinter as mature larvae. Systemic insecticide uptake is linked to root activity, which is strongest in spring and early summer.

Non-chemical controls

Non-chemical measures are foundational and often the first step in integrated management.

Removal and sanitation

Removing and properly destroying heavily infested trees reduces local beetle populations and protects nearby high-value trees.

• Cut and remove trees that show extensive crown decline, multiple years of dieback, or poor structure.
• Chip infested wood to 1 inch or smaller or debark and burn according to local regulations. Do not store or move untreated firewood long distances.
• Stump removal is recommended for heavily infested trees to reduce larval habitat and resprouting.

Timing removal before peak adult emergence reduces the number of beetles that can fly to new hosts.

Wood movement and quarantine practices

Moving untreated ash wood, logs, nursery stock, or firewood spreads EAB. Wisconsin has quarantines and regulations that change by county and over time. Always check with local county extension or state forestry officials before transporting ash material. As a general rule, avoid moving ash wood off-site unless it has been treated, debarked, or reduced to small chips.

Chemical controls

Chemical management with systemic insecticides is the most reliable way to protect high-value ash trees when applied correctly. Choice of product depends on tree size, level of infestation, urgency, and whether the application will be done by a certified applicator.

Key product classes and their properties

• Emamectin benzoate (trunk injection): Considered the most effective long-term option for moderate to high-risk trees. Provides deep phloem protection and typically controls EAB for 2 to 3 years per injection. Results are relatively fast and persist through multiple seasons. Requires application by a professional following label instructions.
• Neonicotinoids (imidacloprid, clothianidin) – soil drench, soil injection, or trunk injection: Effective for prevention and light infestations. Soil applications rely on active root uptake and may be less reliable in compacted or poorly drained soils. Protection typically lasts 1 to 2 years for imidacloprid depending on formulation and tree condition.
• Dinotefuran (foliar spray, trunk injection): Provides rapid knockdown and is useful for trees already showing symptoms or under heavy attack. Its residual effect is shorter, often providing good protection for one growing season. Can be a good emergency option or follow-up treatment.
• Contact and foliar insecticides: Generally not effective for protecting mature trees because larvae are inside the bark. Some foliar applications of dinotefuran or chlorantraniliprole can be used in certain circumstances but are not substitutes for systemic treatments for large trees.

Important: Always follow label directions. Misuse of insecticides risks non-target impacts, regulatory violations, and reduced effectiveness.

Application methods and timing

• Trunk injections: Deliver insecticide directly into the tree’s vascular system and are effective for large trees and for soil environments where root uptake is unreliable. Best done in spring or early summer when sap flow facilitates distribution; many products have specific recommended windows.
• Soil drenches and injections: Require adequate soil moisture and a healthy fine root system. Apply when roots are active (spring and early summer) and avoid during drought or frozen ground.
• Foliar sprays: Can be used on young trees or as supplemental treatment. Not typically recommended as a standalone solution for established trees.

Treatment frequency and cost considerations

• Emamectin injections: Often needed every 2 to 3 years. Cost varies by tree size and applicator, but typical professional injections for mature trees can range from roughly $150 to $500 or more per treatment depending on diameter and local labor rates.
• Neonicotinoids and dinotefuran: May require annual applications or yearly monitoring and re-treatment. Soil treatments are usually less expensive but require consistent scheduling and favorable soil conditions.

Assess the value of the tree, aesthetic and ecological value, and the cost of repeated treatments versus removal and replacement. For very large or specimen ashes, multi-year treatment can be justified.

Biological control

Biological control programs have released parasitic wasps that attack EAB larvae and eggs. Species such as Tetrastichus planipennisi and Spathius agrili have been released in parts of Wisconsin and can establish and reduce EAB populations over time.
Biocontrol is not a stand-alone solution for homeowners who need immediate protection. It contributes to long-term population suppression and may help protect future ash recruitment, but recovery of ash populations using biocontrol alone is slow and variable.

Integrated management strategy for Wisconsin homeowners

Combining methods delivers the best outcomes. A practical stepwise approach:

1. Assess and prioritize: Identify ash trees by value, size, health, and location. Protect high-value landscape or heritage trees first.
2. Monitor and confirm: Look for symptoms and confirm EAB presence if possible. If unsure, consult a certified arborist or local extension service for diagnosis.
3. Decide treatment vs removal: For healthy, high-value trees without severe decline, consider preventive systemic treatment. For trees with extensive crown dieback (greater than 50 percent) or structural instability, removal is usually the safest option.
4. Select treatment and timing: Choose systemic insecticide and application method appropriate to tree size and site. Time applications for spring or early summer when root uptake is best and before adult flight when possible.
5. Plan for the long term: Budget for re-treatment or eventual replacement. Diversify the urban forest by planting non-ash species to reduce future risk.
6. Sanitation and wood handling: If removal is required, dispose of wood responsibly on site or follow state/county guidelines to avoid spreading EAB.

Decision checklist for homeowners and land managers

• Is the ash tree healthy and structurally sound?
• What is the tree diameter at breast height (DBH)? Larger trees cost more to treat and may require professional injection.
• Are there multiple nearby ash trees or a known local infestation?
• Can the soil and root system support soil-applied insecticides?
• Are you willing to commit to multi-year treatments if you choose chemical protection?
• Are local quarantine or wood movement rules in effect that affect disposal?

Use this checklist to make informed, site-specific choices.

Practical takeaways and recommendations

• Early detection matters. Inspect ash trees annually and act quickly when signs are found.
• For high-value trees in Wisconsin, emamectin benzoate trunk injection is one of the most effective longer-lasting options, typically protecting for 2 to 3 years per treatment when applied correctly.
• Dinotefuran provides rapid control for trees already under heavy attack but generally has shorter residual protection.
• Imidacloprid and other neonicotinoids are useful preventive options, but their efficacy depends on tree health, soil conditions, and timing.
• If crown decline exceeds roughly 50 percent or the tree is structurally unsound, removal is usually the best course to reduce hazard and local pest pressure.
• Do not move untreated ash wood. Chip, burn, or otherwise treat wood according to local regulations.
• Consider hiring a Certified Arborist or licensed pesticide applicator for injections or if dealing with large trees, because correct technique, timing, and safety protections are critical.
• Expand species diversity in plantings to reduce future risks from pests and diseases.

Legal and local considerations

Regulations and quarantines change over time. Before transporting ash wood, cutting trees on public land, or conducting large-scale removal, check with your county extension office, municipal forester, or the Wisconsin Department of Natural Resources for current rules and recommended disposal methods. Local programs may offer subsidized removals, biological control releases, or treatment guidance.

Final note

Emerald ash borer management in Wisconsin is a long-term commitment. Combining accurate monitoring, targeted chemical protection for valuable trees, responsible removal and disposal for severely infested trees, and long-term replanting strategies gives property owners the best chance of preserving tree canopy and reducing the impact of this invasive pest. When in doubt, consult a qualified arborist or your local extension service to develop a site-specific plan that follows current state guidelines and pesticide labels.