Homeowners can take steps to save their own ash trees from ash borers. There are several products available to homeowners that claim to control this devastating insect. This article is provided to help homeowners make informed decisions about what to use, what to avoid, and when to call a professional.
ASH BORER LIFE CYCLE.
The Emerald Ash Borer is a beetle as an adult. The adult insect emerges in June or July in Michigan and feeds on the leaves of ash trees before mating and laying eggs on ash bark. The larva emerges and bores through the bark. The larva then feeds under the bark in winding galleries until the next spring. It then pupates to finish its transformation into an adult. The adult exits the pupa and chews its way through the bark, making a D-shaped emergence hole before flying away as an adult insect.
Direct evidence of ash borer presence includes the D-shaped holes, notching of ash leaves, galleries under the bark, and of course finding an adult insect or a larva under the bark. Indirect evidence includes woodpecker activity and damage to the bark as the birds go after the larva under the bark, thinning and defoliation of the tree, starting at the top in most cases.
WHEN TO TREAT
The wise approach to ash borer management is to treat before you see evidence of ash borers. If you have an ash tree and there are ash borers in the area, treat preventively. The old adage about an ounce of prevention being worth a pound of cure is certainly applicable. This is especially true for homeowner applied management options.
If there is evidence of ash borer infestation, treatment may be possible, but homeowner products may not save the tree and a professional treatment may be needed.
1. IMIDACLOPRID. There are several products available in garden centers and hardware stores that contain the active ingredient imidacloprid. Some formulations also have fertilizer. These products can be fairly effective for ash borer prevention in smaller trees, 32 inches or less in trunk circumference. They must be applied every year in the spring and label directions must be followed carefully. Depending on the concentration of active ingredient, the dosage is 1/2 ounce, 1 ounce or 2 ounces of product per trunk circumference inch. The measured amount of product is mixed with water and applied as a drench around the base of the tree and watered in to get it down to the roots. If there is mulch around the tree, it should be pulled back before drenching, so that all of the treatment solution reaches the soil at the base of the tree.
2. ACEPHATE. This insecticide is available in a spray formulation concentrate to be mixed with water and sprayed on trees. It can also be used as a soil injection for systemic control of many insects. It can be very effective as a soil injection or trunk injection when applied by a professional arborist, but has a short duration of action and should be considered only to supplement treatment with longer acting systemic products like imidacloprid when treating trees that are already infested.
Acephate comes in another homeowner formulation, packaged in capsules applied to the trunk. We discuss the method here mainly to discourage the use of this method. These capsules require drilling of several holes in the tree, then tapping the capsules into the holes. This method has been sold as effective treatment for ash borers, but has a number of drawbacks: the duration of action is short, the treatment has to be repeated annually (thus requiring multiple holed drilled every year), and long term effectiveness has not been proven.
3. PYRETHROID SPRAYS. Spraying of trees with synthetic pyrethroids like bifenthrin can be effective if thorough coverage of foliage can be achieved and maintained during the adult phase of the insect (June through August.) This method targets only the adult phase feeding on the leaves. Adults could still fly in from other trees and lay eggs on the bark and thus infest the tree. We discuss this method also to discourage its use. It is difficult to get thorough coverage, especially on large trees, much pesticide is applied to non-target areas by run-off and drift, and the effectiveness is inferior to systemic products.
4. TRUNK INJECTION OF IMIDACLOPRID. Legally, a homeowner could buy the injection equipment and buy injectable imidacloprid and learn to inject it. This would achiever higher levels of control than any of the above approaches. Although expensive and time-consuming, this may be a reasonable approach for someone with a lot of ash trees. You would have to have a willingness to be meticulous and careful in learning and applying this method. We would also discourage this approach, because if you are going to treat the trees with a method that involves drilling the trees, it is best to treat with a product that has two to three year duration of action (TREE-Age, emamectin benzoate.)
5. TRUNK INJECTION OF EMAMECTIN. Emamectin benzoate, brand name TREE-Age, is really the gold standard for ash borer treatment and prevention, especially for trees that are already infested. However, this product is a restricted use pesticide and you must have a pesticide certification to buy it. Applied by a professional, this product will kill and prevent ash borers for two to three years at a 99% effectiveness level. Go to this link and read page 9 to learn about the comparison of various products:
CALL A PROFESSIONAL IF:
1. The tree is over 32 inch trunk circumference (10 inch trunk diameter)
2. The tree has direct or indirect evidence of infestation. In some cases, a professional can save the tree with TREE-Age and then the homeowner can maintain the control with imidacloprid drenches until the tree is over 32 inch circumference.
3. CAVEAT. Insist that the professional uses TREE-Age (emamectin benzoate). Do not consider professional treatment with any other product. Other products may be less expensive, but are definitely less effective. That is, you may save money but lose the tree.