What Are the Treatments for Ash Tree Borers?

Soil-applied Insecticide

• Soil-applied insecticide, with the active ingredient imidacloprid, is applied to the soil via soil drenches or soil injections. The insecticide, which is readily available under various brand names, is available for purchase by homeowners or professional applicators; however, homeowners are limited to the drench formulation of imidacloprid. The drench version of the product is mixed with water then poured directly on the soil near the base of the ash tree. Soil injection requires specialized equipment in order to place chemicals underground directly in the root zone, reducing runoff potential. Soil-applied insecticide is most effective when used on infected trees with a diameter 16 inches or less.

Trunk Spray

• Alternatively, trunks of ash trees are sprayed with an insecticide specifically formulated to treat emerald ash borers, which uses the active ingredient dinotefuran with pentrabark. The insecticide is sprayed on the lowest 6 feet of the trunk using a garden sprayer. When applied correctly, this type of treatment will penetrate and treat the tree trunk without ever entering the soil. Overall, it is an simple treatment that will not harm the long-term health of the tree.

Trunk Injection

• The quickest treatment is the trunk injection method. Using this form of treatment, insecticide containing imidacloprid is physically injected into the tree trunk by a professional using specialized equipment. It can be a useful treatment in situations where other forms of treatment are not practical, such as sites with very wet or compacted soil. There is potential for tree injury, particularly when this treatment is performed on an annual basis.

Canopy Spray

• Canopy sprays are applied via a chemical spray to the trunk, branches and foliage of infected ash trees. This treatment option is designed to kill feeding, egg-laying adult ash tree borers. It is most effective when applied while adult emerald ash borers are most active, which can be difficult to predict. Canopy spray will not treat active infestations under the tree bark. Active ingredients may include permethrin, bifenthrin, cyfluthrin and carbaryl. Be aware, canopy sprays require special equipment and may adversely impact non-intended organisms.

Considerations

• With the exception of trunk injections, which may be effective up to three years, treatments must be repeated annually. For best results, apply treatments after leaves appear in the spring but before borer eggs have hatched. In most locations, this occurs mid-May to mid-June. Begin treating infected ash trees as soon as possible. Relatively healthy tree respond best to treatment. It is most likely too late to treat a tree that has lost more than 50 percent of its crown.