Emerald Ash Borer: Treatment Options and Timing
Current treatment methods for protecting ash trees from emerald ash borer and when they make sense.
Emerald ash borer (EAB) has killed hundreds of millions of ash trees in North America since its discovery in Detroit in 2002. It is now found in 36 states and continues to spread. Here is what arborists need to know about treatment options.
Should You Treat or Remove?
Not every ash tree is worth treating. Treatment makes sense when the tree is:
- In good health with a full crown (less than 20% canopy thinning)
- Structurally sound with no major defects
- In a location where it provides significant value (shade, aesthetics, property value)
- Large enough that replacement would take decades to match (over 12 inches DBH)
If the tree is already in decline (more than 50% canopy loss), treatment is unlikely to save it. Recommend removal instead.
Treatment Methods
Trunk Injection
Emamectin benzoate (sold as TREE-age or TREE-age G4) is the most effective and widely used treatment. It is injected directly into the trunk at the root flare using pressurized capsules. One treatment protects the tree for two to three years.
Trunk injection is done by licensed applicators and costs $8 to $15 per diameter inch. A 20-inch DBH tree costs roughly $160 to $300 per treatment cycle.
Soil Drench or Injection
Imidacloprid (sold as Merit, Xytect, or generic formulations) can be applied as a soil drench around the root zone or injected into the soil. It is less expensive than trunk injection but also less effective on large trees (over 20 inches DBH) because uptake through the roots may not distribute the insecticide evenly throughout the crown.
Soil treatments work best on smaller ash trees (under 15 inches DBH) and should be applied in spring when the tree is actively taking up water.
Bark Spray
Dinotefuran (sold as Safari or Transtect) can be sprayed on the trunk and absorbed through the bark. It provides shorter protection (one year) and works best on trees with smooth, thin bark. Less commonly used than injection or soil drench.
Treatment Timing
Start treatment before EAB arrives or as soon as it is detected in your county. Waiting until you see D-shaped exit holes and canopy thinning means the infestation is already advanced. Early treatment is far more effective than reactive treatment.
Trunk injections are typically done in late spring to early summer when the tree is in full transpiration. Soil applications are done in mid-spring.
Long-Term Commitment
Treating an ash tree for EAB is a long-term commitment. You need to re-treat every two to three years for as long as EAB pressure persists in the area, which could be decades. Make sure the customer understands this before starting a treatment program. The cumulative cost of treatment should be weighed against the cost of removal and replanting.
Sources and Further Reading
- • USDA APHIS (Animal and Plant Health Inspection Service): Federal guidelines on emerald ash borer management and approved treatment protocols
- • International Society of Arboriculture: Professional standards and best practices for ash tree treatment timing and application methods
- • Michigan State University Extension: Research-based recommendations on treatment effectiveness and cost-benefit analysis for ash preservation
- • USDA Forest Service: Comprehensive data on treatment options including systemic insecticides and biological control methods
Try These Free Tools
Put these insights into practice with our free calculators and planners: