Chemicals to Kill Ash Tree Borers

Ash borers are invasive pests that can wreak havoc on your ash trees. If your trees have dead branches in the canopy, thin foliage, split bark and evidence of cream-colored larvae or metallic green adult beetles, you may have an ash borer problem. A variety of chemical insecticides are available to solve the problem. If your ash tree has lost more than half its canopy, it may be too late to start treatment. Trees should be healthy before using insecticides.

Applying a systemic insecticide to the soil in mid-April to mid-May can be effective against ash borers. These insecticides are sucked up by the tree’s roots and distributed throughout the entire tree. Imidacloprid is mixed with water and poured over the soil surrounding the trunk. Avoid applying imidacloprid to extremely wet or dry soil and remove any mulch from around the tree prior to application. This can decrease its effectiveness. To prevent these problems, you may choose to use an injection system to inject imidacloprid two to four inches below the soil’s surface instead. This allows the insecticide to directly penetrate the roots, but this method requires specialized equipment. With either method, it can take four to six weeks to successfully treat the ash tree.

You can also inject Imidacloprid and emamectin benzoate into the ash tree’s trunk to control borers. You will need a systemic insecticide injection system to use this method. Apply the injections just after leaves have fully appeared, between mid-May and mid-June. This method is good if your ash tree is growing on wet or compacted soil. The disadvantage is that trunk injections cause damage to the trunk if they are done every year. Inject trunks early in the day while the soil is still moist as hot temperatures and dry soil can prevent uptake of the product.

Dinotefuran is in the same class of insecticides as imidacloprid and can be sprayed on the bark of ash trees. Spray it onto the bottom five to six feet of the trunk with a garden sprayer on a low pressure setting. Once the bark absorbs the insecticide, it spreads throughout the tree. Use this method if you want a spray that is fast and simple, doesn’t harm the tree and does not allow the insecticide to penetrate the soil.

You can apply some sprays, including permethrin, cyfluthrin, carbaryl and bifenthrin, to the exterior of the tree to prevent ash borers from infesting the tree. These sprays will kill ash borers and their eggs on the surface of the tree, but will not kill larvae beneath the bark. For this method to work, you must spray the entire tree thoroughly. Two applications are often necessary to control ash borers.