Best Ways To Protect Illinois Trees From Emerald Ash Borer

Emerald ash borer (EAB) has killed millions of ash trees across North America since it was first detected. In Illinois the insect is now widespread, and protecting valuable ash trees requires a combination of accurate identification, timely intervention, and long-term planning. This article explains practical, science-based strategies homeowners, municipal managers, and landowners can use to protect trees, slow spread, and plan for replacement where necessary.

How Emerald Ash Borer Attacks Ash Trees

Emerald ash borer is a wood-boring beetle whose larval stage feeds under the bark of ash trees, destroying the tree’s ability to transport water and nutrients.
Signs of infestation appear gradually and may be mistaken for other stresses early on. Left unchecked, EAB kills most untreated ash trees within three to five years of heavy infestation.

Common identification clues

Small D-shaped exit holes in bark approximately 3 to 4 mm across.
Serpentine (S-shaped) galleries visible under the bark when the bark is peeled away.
Progressive canopy thinning and branch dieback starting in the upper crown.
Epicormic sprouting (sucker shoots) on the trunk and main branches.
Increased woodpecker activity that may leave patches of stripped bark.
Vertical splitting of bark on heavily infested trunks.

When and where to monitor

Inspect trees annually in late spring through fall. Canopy thinning becomes more obvious in late summer and early fall.
Focus monitoring on ash trees in high-use areas (streets, parks, yards) and on larger-diameter trees, which are the most valuable and at high risk.
If you find signs, document with photos, note tree location, and contact a certified arborist or local forestry department for confirmation.

Chemical control options: targeted systemic insecticides

Chemical control is the most reliable method to keep high-value ash trees alive where EAB pressure is present. Systemic insecticides are absorbed by the tree and kill larvae feeding in the cambial zone.

Main active ingredients and application methods

Emamectin benzoate (injection). Emamectin is widely considered the most effective and longest-lasting option. It is usually applied by trunk injection and provides 2 to 3 years of control per treatment for most trees.
Dinotefuran (soil drench, trunk spray, or injection). Dinotefuran acts quickly and is useful for trees with active infestation symptoms that need rapid protection. It tends to provide control for a single growing season when soil-applied, though injection formulations may last longer.
Imidacloprid (soil drench or trunk spray). Imidacloprid can be effective as a preventive treatment for smaller trees or when used as part of an integrated program. Soil-applied imidacloprid may require single or multiple season applications depending on soil texture, tree size, and label directions.
Other products. Some other systemic insecticides and formulations are available; product labels and local extension guidance should be consulted.

Important considerations:

Trunk injection tends to restrict active ingredient to the target tree and reduces non-target exposure compared with widespread soil drenches.
For large, high-value trees, emamectin injection by a licensed applicator is typically recommended on a 2- to 3-year cycle.
Dinotefuran is useful when rapid uptake is needed (declining trees), but may need annual application.
Soil-applied products may be less reliable in compacted urban soils or during drought, when root uptake is limited.
Always follow label directions and local regulations. Many trunk injections and concentrated pesticides require licensed applicators.

Choosing the right treatment for your situation

Healthy, high-value mature ash: prioritize emamectin benzoate injection every 2 to 3 years.
Declining ash needing quick suppression to buy time: dinotefuran injection or soil drench can give rapid control; follow up with longer-lasting products.
Small or young ash trees: imidacloprid or dinotefuran soil drench or trunk injection can be cost-effective in the short term.
Trees in sensitive sites (pollinator plantings, waterways): favor trunk injection where possible to reduce off-target effects and consult professionals.

Non-chemical and cultural options

Chemical treatment is not the only tool. Cultural practices, sanitation, and strategic removal help manage the landscape-level problem.

Removal and disposal

Remove trees that are more than 50 percent dead, structurally unsafe, or less cost-effective to save than to remove.
When removing infested trees, chip or debark and burn per local guidance. Do not transport infested firewood long distances; wood movement spreads EAB.
For urban areas, stagger removal and planting to maintain canopy cover and reduce heat-island effects.

Planting and species diversification

Replace removed ash with a diverse mix of species to avoid future single-species losses. Diversity by genus, species, and age reduces vulnerability.
Recommended replacement approach: combine native oaks, maples (select disease-resistant species), honeylocust, hackberry, ginkgo, river birch, and understory trees suitable to your site conditions.
Plant properly: choose appropriate species for soil, drainage, and space; plant at correct depth; mulch correctly; and water during establishment.

Pruning and tree care

Maintain tree vigor through proper mulching, watering during drought, and correct pruning practices.
Avoid unnecessary root disturbance or soil compaction around tree root zones.

Biological control and community programs

Biocontrol agents (parasitic wasps) have been released in parts of Illinois to help reduce EAB populations. While these natural enemies can help slow spread and increase long-term suppression in forested landscapes, they are not a reliable stand-alone solution for protecting individual high-value urban trees today.
Municipal and county forestry programs often run coordinated efforts that include detection, targeted treatments of public trees, and community outreach. Homeowners should coordinate with local programs where available.

Making decisions: prioritize and plan

Managing EAB involves prioritization based on tree value, health, and the resources available. The following numbered checklist helps homeowners decide what to do.

Inventory and assess: identify all ash trees on your property, measure DBH (diameter at breast height), and assess health and location value (shade, aesthetics, structure).
Prioritize: classify trees as high-priority (large shade tree in yard or street), medium (small yard ash), or low (dying or near replacement).
Consult a professional: for high-priority trees, get a certified arborist evaluation and treatment estimate.
Choose a strategy: treat high-priority healthy trees; monitor and consider treatment for medium trees; plan removal and replacement for low-priority or dying trees.
Implement and monitor: if you treat, follow label and applicator recommendations and re-check trees annually. For removals, plan replacements with diverse species.

Monitoring and long-term follow-up

Re-inspect treated trees annually for canopy condition and new signs of infestation.
Follow retreatment intervals recommended by your applicator and product label (for example, emamectin every 2 to 3 years; dinotefuran or imidacloprid may require annual or biennial applications depending on soil and tree size).
Record treatments, tree condition, and dates to track effectiveness.

Safety, regulation, and environmental considerations

Pesticide labels are legal documents. Follow label instructions for rates, application methods, required equipment, and restrictions.
Many professional injection products require licensed applicators. Homeowners using over-the-counter products should read labels and be cautious around flowering trees that attract pollinators.
Minimize non-target impacts by preferring injections over broad soil sprays when possible, especially near pollinator plantings or water bodies.

Practical takeaways for Illinois landowners

Start by identifying and monitoring ash trees now; early detection gives you the most management options.
For high-value, healthy ash trees, invest in professional treatment–emamectin injections every 2 to 3 years offer the most reliable long-term protection.
Use dinotefuran for rapid suppression when you need immediate control, and imidacloprid for smaller trees or as part of a multi-year plan.
Remove and properly dispose of heavily infested or hazardous trees, and do not transport untreated firewood.
Replace removed trees with a diverse mix of species suitable for Illinois soils and climate to increase long-term urban forest resilience.
Work with your municipality, extension service, or certified arborist for coordinated responses and to learn about local programs or biological control releases.

By combining accurate detection, appropriate use of systemic insecticides, sensible removal and replacement planning, and community coordination, Illinois homeowners and land managers can protect valuable ash trees and maintain urban and rural canopy health in the face of emerald ash borer.