One of the most destructive tree pests in North America has reached all 99 counties in Iowa.
Emerald ash borer is an invasive beetle that attacks and kills ash trees. The adults eat leaves while larvae feed on the living plant tissue under the bark.
Iowa’s first confirmed detection was in 2010 in Allamakee County. Iowa Department of Agriculture and Land Stewardship (IDALS) officials recently collected insect samples from a diseased tree in Emmet County, the last hold-out. The U.S. Department of Agriculture confirmed that it was emerald ash borer.
While widespread, state officials say infestations are isolated in some counties. Since the invasive beetle cannot fly long distances, people can help slow its spread by limiting the movement of ash firewood and timber.
Detection, prevention and treatment
Ash trees within 15 miles of a known infestation are considered at high risk of attack. Experts say preventative insecticide treatments can help protect healthy ash trees. But once there’s significant damage, the tree is unlikely to recover.
“Emerald ash borer tends to attack towards the top third portion of the tree first, and over time, it progresses down,” said Mike Kintner, an entomologist and the emerald ash borer and spongy moth outreach and regulatory coordinator with IDALS.
Emerald ash borer tends to attack towards the top third portion of the tree first.Mike Kintner, entomologist
Kintner said landowners should look out for dying and dead branches at the top of ash trees. This is easiest to spot in summer when healthy branches leaf out.
“During the winter months, you can still find EAB in trees even though the leaves are off,” Kintner said. “Woodpeckers will come in if a tree’s infested.”
Woodpeckers fleck off the bark to eat the larvae underneath, Kintner said, adding that this happens in the top third of tree in the early stages of an infestation.
Other signs include D-shaped exit holes on branches and trunks when newly developed adults emerge and S-shaped feeding tunnels from larvae. Over time, this causes the bark to dry out and fall off, Kintner explained.
“[The larvae] feed right below the bark surface, between the wood and… the vascular system of the tree. And that's really why the trees are dying out and being impacted, because they're damaging that area,” Kintner said.
Infested ash trees tend to die within two to four years. As landowners and communities consider replacing these trees, Kintner and other state officials recommend planting with diversity in mind.
Ash trees make up nearly 20% of total street tree canopy in the average Iowa community. In some communities, they represent over 50%.
