New emerald ash borer infestation discovered in Iowa

Chloe Carson
Iowa Department of Agriculture and Land Stewardship
Emerald Ash Borer

Emerald ash borer has been found in Iowa's Dickinson and Humboldt counties for the first time. The invasive, ash tree-killing insect from Asia has now been confirmed in all but eight of Iowa’s 99 counties since its original detection in 2010.

Larvae were collected by Iowa Department of Agriculture and Land Stewardship staff just outside the eastern city limits of Arnolds Park (Dickinson County) and rural Dakota City (Humboldt County). Federal identification confirmed the samples positive for the bug.    

The adult beetles of this insect feed on ash leaves, causing very little damage. It is the cumulative damage by larval feeding on the inner bark that eventually kills ash trees. The feeding cuts off the tree’s ability to transport water and nutrients, typically killing a tree within two to four years. Emerald ash borer is a significant threat to all native ash species.

Indicators of an infestation may include canopy thinning, leafy sprouts shooting from the trunk or main branches, serpentine (“S”-shaped) galleries under the bark, bark splitting, woodpecker damage and 1/8-inch D-shaped exit holes.

“Because woodpecker damage can be a sign emerald ash borers have infested an ash tree, we receive a number of calls during the winter and early spring,” said Mike Kintner, Iowa Department of Agriculture and Land Stewardship EAB and spongy moth coordinator. “These latest new county detections were the result of green industry professionals alerting our department about the possibility of infested trees based on the woodpecker damage they observed.”

While emerald ash borers can travel locally by natural means, long distance spread of this insect is attributed to people moving infested material, including firewood. People are reminded to use locally sourced firewood where it will be burned to help limit the spread of emerald ash borers and other invasive pests.

Now is the time to decide a course of action for ash trees at risk of an emerald ash borer attack (within 15 miles of a known infestation). Landowners and managers can choose to wait and see what happens, remove declining ash trees and replace them with other species or use preventive insecticide treatments to preserve and protect valuable and healthy ash trees.

Spring, from mid-April to mid-May, is the best time to treat for emerald ash borers. Insecticides are most effective when the ash tree is actively growing, and uptake is at its peak. Tree service companies can apply insecticide trunk injections through the summer if soil moisture is available.

The State of Iowa continues to track the spread of emerald ash borers on a county-by-county basis. Before a county can be declared positive, a life stage of the insect must be collected and confirmed. Anyone who suspects an infested ash tree in a county not currently known to be confirmed with emerald ash borers is encouraged to contact one of the following:

  • Iowa Department of Agriculture and Land Stewardship, State Entomologist Office, 515-725-1470.
  • Iowa State University Extension and Outreach, Entomology, 515-294-1101.
  • Iowa Department of Natural Resources, 515-725-8453.

Additional information on emerald ash borers, including a county detection map, can be found at iowatreepests.com.