MDA confirms emerald ash borer detections in Pine and Renville counties; urges early detection and management

Jonathan Ostes, Emerald Ash Borer technical assistance coordinator for the Minnesota Department of Agriculture, said the agency recently confirmed emerald ash borer (EAB) detections in southern Pine County near Rock Creek and in Renville County near Danube, just west of Olivia. MDA staff reviewed the insect’s life cycle, the signs surveyors use to find infestations, and steps homeowners and cities can take to manage trees once EAB is nearby.

The finding adds to a multi‑state invasion: Ostes said EAB is known in 38 U.S. states and five Canadian provinces and was first detected in Minnesota in 2009 in the South St. Anthony Park neighborhood of St. Paul. He emphasized that the beetle’s lifecycle and cryptic early symptoms mean a tree can be infested for years before visible decline, so communities on the “leading edge” should prepare now.

Ostes described the key diagnostic signs to watch for: S‑shaped larval galleries beneath the bark, dime‑sized shallow woodpecker holes and ‘blonding’ where woodpeckers strip outer bark. He advised that adults are active roughly May through September and that larvae tunnel in the mid‑to‑upper canopy; pull‑back of bark in winter with binoculars can reveal galleries.

For homeowners and municipal foresters considering options, Ostes said there are two main responses: targeted removals and insecticide treatments. He recommended removing poor‑condition or poorly sited trees before infestations arrive, and using targeted removals for trees showing clear signs. "If you want to save a large, healthy shade tree, treatment can be cost‑effective over time," Ostes said, explaining that systemic insecticides are often effective if applied correctly and when trees have no more than about 30% canopy decline.

On treatment specifics, he said emamectin benzoate is commonly used by tree‑care professionals as a trunk injection and provides roughly two years of protection; homeowner options include soil drenches such as imidacloprid but labels and pollinator risks must be followed. Ostes gave an approximate homeowner cost of about $7–$10 per diameter inch for treatment and stressed that some chemicals require annual reapplication while others last two years.

Ostes urged early detection and reporting to slow spread and reduce long‑term costs to cities and residents. "Don't move firewood and buy where you're gonna burn it," he said, advising residents to photograph suspected symptoms and submit precise locations via the Department of Agriculture’s 'report a pest' form so MDA can follow up.

MDA will post the recorded presentation and maintain the agency’s EAB status map online; Ostes also announced three field workshops — in Brainerd, Dilworth (near Moorhead) and Jordan — where participants can see infested trees in person.