Emerald Ash Borer Update: Should Iowans Start Treating Their Ash Trees?

At this time, there is no need for insecticide treatments for emerald ash borer anywhere in Iowa. The emerald ash borer (EAB), Agrilus planipennis, has been found 85 miles from Iowa in Peru, IL. As EAB moves closer to, and into Iowa, this recommendation may change as we learn more about the known infestation areas and the ever-changing status of control options. But for now, any application of insecticides to ash trees for EAB control is a waste of time, money and resources.

The rationale behind this position is as follows:

  • Treatment in advance of the presence of the pest is not justified. As an analogy, a person would not use chemotherapy before they were diagnosed with cancer. Premature use of pesticides is expensive, may cause harm to the applicator and the environment, and might be a violation of the product label.
  • Control of wood-boring insects is challenging and results have been variable. Research has shown that some insecticides may be capable of protecting trees from emerald ash borer but success cannot be assured. No treatment is 100% effective against this pest at this time.
  • Chemical treatment must be done at least yearly; some regimens recommend applications two times a year. The landowner must commit to yearly or biyearly treatments for an interminable number of years.
  • Some particularly valuable trees in apparent good health may be worthy of consideration for a treatment program, especially smaller trees (<10 inches in diameter) growing on good sites and without trunk injuries (lawn mowers, string trimmers). Treatment is recommended only after an EAB infestation is confirmed within your township or within 15 miles away (close enough to put your tree at risk).
  • Even if you treat your ash tree(s) for years before the emerald ash borer arrives in Iowa, this does not guarantee the tree(s) will be spared from containment cutting operations by regulatory agencies that will enforce state and federal quarantine rules.

Should Iowans Remove Ash Trees?

We do not recommend removing healthy ash trees to prepare for the EAB infestation. Instead, enjoy the ash resource while you can. We do advise checking the condition of ash trees and note those that are declining or otherwise in poor health. If more than 50% of the ash tree crown is dead or if the trunk has large wounds or areas of dead bark the tree is at high-risk for potential infestation by EAB. Such trees should be considered for removal and replacement. For these high-risk trees replacement may be a better use of money than treating.

When replacing ash trees consider species diversity and site conditions. Click here for a list of recommended trees for the Iowa landscape:

If you have questions about your ash tree or insect pests of trees please contact ISU Extension Entomology, the Iowa Department of Agriculture and Land Stewardship, the Iowa Department of Natural Resources, your local nursery dealer or certified arborist.

Emerald Ash Borer, adult beetle.  Photo by  David Cappaert, Michigan State University,Emerald Ash Borer, adult beetle. Photo by David Cappaert, Michigan State University. http://www.bugwood.org/


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