Emerald ash borer confirmed in all 99 counties

DES MOINES — Emerald ash borer, an ash tree-killing insect, has now been confirmed in all of Iowa’s 99 counties.

Insect samples were collected from a declining ash tree in Armstrong earlier this month by staff from the Iowa Department of Agriculture and Land Stewardship and sent to the United States Department of Agriculture Animal and Plant Health Inspection Service for confirmation.

With positive confirmation in Emmet County, there are no remaining counties in Iowa without a detection.

Emerald ash borer is a non-native, wood-boring insect threatening all species of ash trees. The adult beetle is about 1/2 inch long and metallic green.

The larval stage of this insect tunnels through the wood just beneath the bark of ash trees, cutting off the tree’s ability to transport water and nutrients. The cumulative damage typically kills a tree within two to four years after becoming infested.

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.

The borer was unknown to North America until its discovery in southeast Michigan in 2002. The invasive, ash tree-killing insect from Asia has now been found in 37 states. The emerald ash borer was first discovered in Iowa in Allamakee County in 2010.

Landowners with ash trees on their property should begin to consider a course of action for at-risk trees, which are generally those within a 15-mile radius of a known infestation.

Landowners and managers can 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.

The best time to treat for the borer is in the spring, from mid-April to mid-May. 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.

Iowa State University Extension and Outreach has produced a publication about ash borer treatments. For more information, download Emerald Ash Borer Management Options.

Because the emerald ash borer and other invasive pests can unknowingly hitchhike in firewood, people should use firewood locally sourced from the area where it will be burned.

More information can be found at iowatreepests.com.