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Emerald Ash Borer Confirmed in Plymouth County

May 31, 2023

Contact: Don McDowell, Iowa Department of Agriculture and Land Stewardship, [email protected]

DES MOINES, Iowa – Federal identification has confirmed the presence of the emerald ash borer in Plymouth County for the first time. Insect samples were collected by the Iowa Department of Agriculture and Land Stewardship from an ash tree in Remsen after an area tree service alerted the department of a tree with symptoms of an infestation. EAB is a non-native, wood-boring insect threatening all species of ash trees.

The adult beetle is approximately one-half 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.

EAB 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 36 states and confirmed in all but two of Iowa's 99 counties. The only remaining counties in Iowa without a detection are Emmet and Palo Alto. In 2010, EAB was first discovered in Iowa in Allamakee County.

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 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 EAB 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 EAB treatments. For more information, download Emerald Ash Borer Management Options.

While EAB travels only short distances on its own, people aid in its long-distance movement. Since this insect can unknowingly hitchhike in firewood, people are reminded to use locally sourced firewood where it will be burned to keep it from being transported to new areas.

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 either of Iowa's two remaining counties (Emmet and Palo Alto counties) is encouraged to contact one of the following:

More information about EAB, including detection maps, is available at

Shareable map: Emerald Ash Borer Treatment Consideration Areas in Iowa

Shareable map