Emerald Ash Borer Discovered in Humboldt County

Emerald ash borer has been found in 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.

EAB 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 EAB.

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. EAB 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 EAB has 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 EAB infested trees based on the woodpecker damage they observed.”

While EAB 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 EAB and other invasive pests.

Now is the time to decide a course of action for ash trees at risk of EAB 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 EAB. 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.

See Iowa State University Extension and Outreach publication ENT57, “Emerald Ash Borer Management Options,” for more details about EAB treatment.

The State of Iowa continues to track the spread of EAB 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 EAB 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 EAB, including a county detection map, can be found at


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