By Jeff Palmer
The Emerald Ash Borer (EAB) is an invasive pest introduced from Asia that attacks ash trees (Fraxinus spp.) This wood-boring beetle was found in Detroit and Ontario, Canada in 2002, and continued to spread into neighboring states and, eventually, to other areas of the United States and Canada, killing over 30 million trees.
The adult is a small, metallic-green beetle only 10-15mm in length and about 3mm in width. The larvae live under the bark of the tree and feed in the vascular cambium, eventually girdling the tree. The adults typically emerge around June, leaving D-shaped exit holes in the bark. This ash tree insect briefly feeds in the canopy before reproducing and laying eggs in the twigs and branches.
Since its discovery in 2002, Emerald Ash Borer has been found in Michigan, Illinois, Indiana, Iowa, Kentucky, Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin, Ontario and Quebec.
EAB larvae live under the bark and feed on the vascular tissues. Larvae create meandering galleries through the phloem, vascular cambium and etch the xylem, effectively girdling the tree. The tree responds by sprouting new (epicormic) branches below the disrupted tissues. Dieback of the canopy is a symptom of EAB larval infestation, and as many as one half of the branches may die back as infestation progresses. The bark will split over dead vascular tissues, and trees may die within only two years of the onset of symptoms.
Independent studies strongly recommend that treatments be applied early, before extensive disruption to the vascular tissues occurs. Dieback symptoms should be less than 40 percent. For best outcome, Arborjet recommends treatment when EAB is detected in your area, but trees still appear healthy. Treat ash with either imidacloprid or TREE-äge insecticide (emamectin benzoate). The comparatively large vasculature in ash trees will readily move imidacloprid upward into the canopy. TREE-äge is more viscous and will take slightly longer to inject, but will provide a longer residual effect. Both TREE-äge and imidacloprid will kill the EAB larvae inside the tree.*
See labels for dosage rate based on tree size.
When to treat
Treat ash if EAB is reported in your area. Do not wait for visible dieback in the canopy, as there is a significant delay between disruption to the vascular tissues and expression of symptoms in the canopy. Delaying EAB treatment could result in canopy dieback or tree loss.
Applications can be made in the spring, about 30 days prior to expected adult emergence; however, treatment may be applied during the growing season (May through July) to protect trees. Uptake of formulation is fastest when trees are actively transpiring, after they have developed a full canopy.
EAB treatment in the spring will prevent the adult beetles from feeding and laying eggs in the tree, whereas summer treatment will kill the larval stage of EAB feeding under the bark. Make summer treatment applications in the morning when temperatures are moderate. If soil is dry, water trees prior to treatment.
Injection in the fall (after leaves color) can protect the tree for the following season. Fall is a great time for injection because the weather is generally cooler and wetter, ideal for quick uptake.
Trees need to be closely monitored for symptoms of EAB as infestation builds in your area. In general, applications are not made more than once a year. Specific insecticide formulations for EAB may provide 2 years of activity.
What to Expect After Treatment
Trees will recover from infestation and will be protected from EAB. Imidacloprid will kill the EAB larvae under the bark and deter adult feeding on the treated tree. TREE-äge will kill the EAB larvae under the bark as well as adult beetles that feed on the tree.
A single application of imidacloprid will provide control of EAB for a full year. TREE-äge will provide 2 years residual control.
The long-term prognosis for trees that are treated early (i.e., before vascular injury) is very good to excellent. Tree recovery from an established infestation is relative to the severity of the infestation at the time of treatment.
Jeff Palmer is with Arborjet, Inc., which develops environmentally responsible trunk injection formulations that protect trees from a variety of insects, diseases and malnutrition. Jeff is a graduate of the School of Forestry at the University of Minnesota, and has been involved with identifying, diagnosing and providing solutions for urban landscape and forest issues for nearly 23 years.
* Note: Always read and follow label instructions before buying or using these products. The instructions contain important conditions of sale, including limitations of warranty and remedy. TREE-äge insecticide is a restricted-use pesticide and must only be sold to and applied by a state certified applicator. TREE-äge is not registered for use in all states. Please check with your state or local extension service prior to buying or using this product. TREE-äge is a registered trademark of Arborjet, Inc.
Editor’s Note: According to the Coalition for Urban Ash Tree Conservation, dinotefuran is also effective for treatment of EAB, and can be soil applied or applied via systemic basal trunk bark spray.