Willmar, Minnesota, braces for inevitable arrival of emerald ash borer (2025)

WILLMAR — Just one year ago, Paul Tinklenberg and three co-workers made a trip to Jordan, Minnesota, for a University of Minnesota Extension-sponsored event where they saw firsthand what an emerald ash borer infestation looks like.

“Some of those things that we saw on that day, I have seen in town,” said Tinklenberg, a foreman with the Willmar Public Works Department.

The very early signs of a potential infestation, when the bark on an ash tree starts turning pale in color, known as “blonding,” is showing up in Willmar.

“Seeing quite a bit of it around town,” said Tinklenberg. “It tells me we’re in the early stages.”

Contributed / David Cappaert, Bugwood.org

While an emerald ash borer infestation has not been officially confirmed in Willmar, it could be coming soon. Field inspectors with the Minnesota Department of Agriculture have the area on their list of places to visit this year, according to Tinklenberg.

The pests' arrival in Willmar has essentially been anticipated ever since the beetle was first found in Minnesota in 2009, according to Justin DeLeeuw, Public Works director for the city. The department began informal conversations to plan for what to expect around that time.

A May 2022 confirmation by the Minnesota Department of Agriculture of emerald ash borer in areas near Nest Lake and in Spicer emphasized that the matter at hand was "when" the unwelcome bug would show up in Willmar, rather than "if."

There’s a lot at stake for a community which benefits greatly from its urban forest.

The Public Works Department estimates that there are 12,000 trees on public boulevards in the community, and that roughly 6,000 — or half of them — are a variety of ash.

There is no estimate for the number of trees in city parks or in the city as a whole, but Tinklenberg and DeLeeuw believe ash trees represent one-quarter or possibly one-third of the total.

Contributed / Minnesota Department of Agriculture

The ash trees in Willmar are predominately large, mature trees. DeLeeuw said the city planted most of its ash trees in the 1950s, '60s and '70s. These trees have large canopies that provide welcome shade and help reduce cooling costs for homes and other structures. The trees improve air quality and contribute to the attractive appearance of parks and residential areas alike.

They will soon become a problem. Once infected, an ash tree can die in as little as two years, but more often in four or more years, according to information from the Minnesota Department of Agriculture.

The challenge is identifying infected trees as early as possible, because the timing matters for their removal, according to Tinklenberg.

Once an ash tree dies, it dries very quickly and becomes brittle, making it a safety hazard and a challenge for removal. No matter how well a tree cutter notches a brittle tree for removal, it’s impossible to predict how a branch or trunk will fall.

In anticipation of the emerald ash borer's arrival, the Public Works Department has been prioritizing the removal of ash from boulevards and parks when it identifies trees that should be removed.

Trees are removed for a variety of reasons: Safety comes first, and trees with visible splits or dead branches that could fall are marked with a yellow "X" and removed.

Contributed / Willmar Public Works

The 6,000 ash trees estimated to be on boulevards is down from 7,000 that were estimated to be present some years ago, DeLeeuw and Tinklenberg noted.

City crews removed 250 trees last winter, and about the same number the winter before. The past two winters did not require as many hours of snow removal work, allowing more time for tree removal than is usually the case.

Each year, the crew also plants 175 trees to replace those lost. New trees are spaced farther apart than was the case years ago, they said. They select trees that fare well in Minnesota soils and climate, including a disease-resistant elm hybrid, as well as oak, linden and hackberry.

Contributed / Willmar Public Works

While many people like to plant maples to replace ash, Tinklenburg and DeLeeuw do not recommend it. Maples like acidic soils, and do not thrive in the alkaline soils found here. Their root structure also tends to be hard on sidewalks and curbs, making them undesirable for boulevard locations, they said.

There is no way to predict just how aggressively the emerald ash borer will decimate Willmar’s ash tree population. Once an infestation is underway in earnest, it could kill a majority of the ash in about a 10-year time frame.

It’s the emerald ash borer larvae that cause the damage that eventually kills the trees. The larvae destroy the vascular system of the trees. They leave S-shaped tunnels in the tree. Because they live under the bark, there are few outward signs of their damage until it’s too late.

Woodpecker activity is usually the first noticeable sign of an infected tree, and it generally becomes noticeable only in the second year. By year three of an infestation, there will be signs of bark splitting, and in year four, the thinning of the upper canopy becomes evident.

There is an effective treatment to save ash trees if it is begun early enough. Trees treated with an insecticide known as emamectin benzoate are protected for two to three years.

The city had looked into its options for treating trees, but quickly discovered that it would be cost-prohibitive due to the large number of trees, according to DeLeeuw and Tinklenberg.

Residents are encouraged to contact area nurseries and tree services to explore their options for removing or treating ash trees, as well as for replacement trees.

The city of Willmar has a partnership with Tree Trust to provide residents in the city limits with 3- to 8-foot trees at a reduced cost of $50. The Kandiyohi Soil and Water Conservation District also has a tree distribution program.

Tom Cherveny / West Central Tribune