AMES, Iowa – Iowans who want to protect their ash trees have options for a brief time this spring. However, the options apply only to valuable and healthy ash trees within 15 miles of a known infestation of emerald ash borer.
The emerald ash borer has been detected in 45 counties in Iowa. Unprotected ash trees will be killed by EAB as it moves through the state.
From mid-April to mid-May landowners can apply a soil drench or a granular product around the base of an ash tree that is 20" diameter (60" circumference) or smaller, says Mark Shour, an entomologist with Iowa State University Extension and Outreach.
Other treatments by certified commercial pesticide applicators could be made later. A basal trunk spray to the lower 5 feet of an ash tree can be applied from mid-May to mid-June for trees 23" diameter (69" circumference) or smaller. The window for injecting the trunk of an ash tree is wider, from initial full canopy until the end of August, Shour said.
Full details are available in the Iowa State University Extension and Outreach publication “Emerald Ash Borer Management Options,” available in English (PM2084) and Spanish (PM2084S). Both versions are available for free download from the Extension Store, https://store.extension.iastate.edu/.
“The insecticide products listed in this publication work best as preventive treatments for healthy ash trees planted along streets or in yards or parks," Shour said. "Healthy trees have full crowns, elongating branches and bark held tightly to the trunk/branches. It is not practical or cost effective to treat woodlot trees where timber production is the primary goal."
“If an ash tree is declining, storm damaged, or growing in a limited site, has loose bark, or if the cost of treatment will exceed the landscape value, replace the tree with an alternate species rather than treat,” Shour added.
For more information about EAB, its treatments and alternative tree species to replace ash trees, contact any of the following ISU Extension and Outreach specialists: