Ash trees are very common on our lawns and parkways and most species, particularly white ash and green ash, are native to Illinois forests. In recent years our ash trees have been threatened by an infestation of the emerald ash borer (EAB). The emerald ash borer is a small, metallic green beetle native to Asia. Though it was first found in Michigan in 2002, it is likely that a beetle population had been established in the Detroit area prior to that time. Besides Michigan and Illinois, the emerald ash borer has been found in Ohio, Indiana, Virginia, Maryland, and Ontario, Canada.
The Problem: The adult emerald ash borer emerges in May - June, and the female lays numerous eggs in bark crevices and between layers of bark. The eggs hatch in 7-10 days and larvae bore into the tree where they chew the inner bark, creating a winding pattern in the wood as they feed. This cuts off the flow of water and nutrients in the tree, causing dieback and death. Adult beetles emerging from trees will leave a very small, 1/8 diameter distinctly “D” shaped exit hole that may appear anywhere on the trunk or upper branches. Since 2002 more than 15 million ash trees have been killed by emerald ash borers.
The Appearance of Infected Trees: The most visible sign of infestation is crown dieback, which appears after the first year. Branches at the top of the crown will die and more branches will die in subsequent years. Typically the tree will be completely dead in about three years, though suckers will sprout from the base of the tree and on the trunk. The bark may also split vertically and woodpeckers may feed on the beetle leaving visible damage on the bark.
Removal of Parkway Ash Trees: About 20% of our parkway trees in La Grange are ash, and already sixteen have been removed. La Grange forester Don Wachter has identified another 50 trees for removal, beginning with those most seriously infected and replacing them with alternative trees like oak. Infected trees have been found on 7th, 9th, and South Kensington Avenues. After ten years the village estimates that La Grange will have no more parkway ash trees.
Treatment Options for Residents with Ash Trees: Property owners can apply chemical treatments to their trees, but these only prolong the life of a tree for a few years. Once infected, the trees will ultimately die. The active ingredient in most treatments for ash trees, imidacloprid, has been approved by the EPA, but is not without risk to the environment. Imidacloprid may be toxic to bees and has been linked to Colony Collapse Disorder, a phenomenon in which bees from a beehive colony abruptly disappear. It may also be toxic to sparrows and pigeons. In addition, imidacloprid treatments can soak into ground water or, if sprayed, can drift into our homes.
Infected trees may also be professionally treated by using preventive bark and foliage cover sprays. These products, although approved for use by the EPA, can be toxic to fish, cats, and bees. These products may extend the life of the tree, but will not cure it. Homeowners should inform the Public Works Department if they want to apply any insecticide, either on their own or with the help of a professional, to a parkway tree.
What We Can All Do:
- Don’t move firewood. Humans unknowingly contribute to the spread of EAB when they move ash logs. EAB larvae can survive hidden under the bark of firewood. Be sure to use all firewood in the cold months so that no hidden EAB larvae or adults can survive on logs left through the spring.
- Visually inspect ash trees. Early detection is a key factor. Look for dead and dying branches at the top of the tree’s crown, a D-shaped exit hole on the trunk, or shoots sprouting from the base of the tree and from the trunk. The bark may split vertically.
- If trees display any sign or symptom of EAB infestation, contact the village if it’s a parkway tree. Remove infected trees on your property. Although insecticides may prolong the life of the trees, their potential to harm bees, animals, and humans as well as our land, air, and ground water suggests the costs outweigh the benefits.
For More Information:
- Beyond Pesticides Fact Sheet
- Sierra Club Canada