RIVER FALLS -- Over 25 years after Dutch elm disease hit River Falls, the city and subsequently Pierce County is again facing the demise of a tree species. This time thanks to the destructive emerald ash borer.

The presence of the pest in River Falls was confirmed in July on private property, marking the first appearance in Pierce County, although River Falls has been preparing for the infestation for over a decade.

Neighboring communities including Hudson are already officially bitten, and other municipalities are gearing up their action plan ahead of confirmed presence.

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River Falls city forester Nathan Croes said he had hoped for a few more years of being borer-free in the city.

In just three to five years, River Falls could see the pest spread to its peak.

“It’s here and it’s not going to go away,” Croes said at an Oct. 8 River Falls City Council meeting.

The Nebraska Forest Service identified approximately 20 other insect species that look similar to the infamous emerald ash borer. The half-inch-long beetle has a metallic green shell and is only associated with ash trees. River Falls city forester Nathan Croes said it is actually rare to find an adult beetle in the ash trees, as about 3/4 of the bug's life cycle remains undetectable in ash trees. File photo
The Nebraska Forest Service identified approximately 20 other insect species that look similar to the infamous emerald ash borer. The half-inch-long beetle has a metallic green shell and is only associated with ash trees. River Falls city forester Nathan Croes said it is actually rare to find an adult beetle in the ash trees, as about 3/4 of the bug's life cycle remains undetectable in ash trees. File photo

The council reviewed the first reading for a new tree ordinance replacing the outdated Dutch elm disease plans and including updates for emerald ash borer. The ordinance outlines the city’s responsibility and right to inspect and remove ash trees on public and private property that might become a hazard.

Croes said removing ash trees early is the safest recommendation as infested ash trees become brittle when dying and difficult to remove over time.

“We haven’t planted one since 2004 and have known this was coming,” Croes added.

River Falls has approximately 8,000 total trees on public property. About 25% of those are ash trees. This number does not reflect any private property ash trees.

The trees where the insect was detected have been removed, and monitoring and select-cutting ash trees is underway. Larger trees that provide significant benefit to public property will be systemically chemically treated, but most smaller trees less than 12 inches in diameter will be removed and eventually replaced.

This means the tree-lined road ways of Lawson Lane, Golf View Drive, Sunset Lane and Roosevelt Street in River Falls might look a lot different in the coming years as the city plans for ash trees to be put to rest.

One of the first ash trees in River Falls to be found infested with Emerald Ash Borer July 2019. City forester Nathan Croes said the trees on private property were about to be taken down by a local contractor, but Croes was asked to inspect the trees after finding unusual signs.  Photo courtesy of City of River Falls Urban Forestry
One of the first ash trees in River Falls to be found infested with Emerald Ash Borer July 2019. City forester Nathan Croes said the trees on private property were about to be taken down by a local contractor, but Croes was asked to inspect the trees after finding unusual signs. Photo courtesy of City of River Falls Urban Forestry

Replanting various types of trees would protect the city from losing thousands more trees to a species-specific disease or infestation in the future, Croes said.

More information about River Falls’ ordinance, emerald ash borer plan and answers to private property owner questions can be found by searching “emerald ash borer” on the city of River Falls website.

The bug’s big national, local spread

The emerald ash borer initially weaseled its way into North America through packaging materials transported from Asia to Michigan in 2002. The species has now spread to every state east of Colorado except Florida, Mississippi and North Dakota, according to the United States Department of Agriculture.

Most of southeastern Wisconsin has been bitten by the bug already, while most of the northern half remains untouched.

Brad Johnson, a regional urban forestry coordinator with the Wisconsin Department of Natural Resources, focuses on western Wisconsin’s forestry division. He said Pierce County could see the invasive species spread two or fewer miles each year.

This Delavan blue ash tree. photographed in 2013 in southeastern Wisconsin where the emerald ash borer is widely spread, features the signature D-shaped exit holes created by the adult emerald ash borer. Wisconsin Department of Natural Resources photo
This Delavan blue ash tree. photographed in 2013 in southeastern Wisconsin where the emerald ash borer is widely spread, features the signature D-shaped exit holes created by the adult emerald ash borer. Wisconsin Department of Natural Resources photo

Although the bug rarely flies long distances, once it has found a group of ash trees, the pest’s presence is inevitability mobile because humans transport wood housing the species, River Falls city forester Nathan Croes said. As of last year all Wisconsin counties are now quarantined for the emerald ash borer, and though firewood can be moved between quarantined counties, the Department of Agriculture, Trade and Consumer Protection strongly discourages doing so due to the risk of transporting other pests and diseases.

Hudson is already dealing with the bug and other communities in St. Croix County are acting on their preparedness plan.

Hudson

Emerald ash borer was first confirmed in the city in July 2018, off Crest View Drive and Carmichael Road, as well as in the Town of Hudson along Fraser Lane.

The city has reached its goal of treating 10% of the ash population in city parks and right of ways, said Parks Director Mike Mroz.

Like River Falls, Hudson has been working to prepare for the invasive species for years. The Urban Forestry Board completed a full inventory of public trees, and in 2012 instituted a plan to deal with the emerald ash borer.

Hudson continues to remove and replace areas with high densities of ash trees.

High-risk trees were the first to be removed, before foresters focuseson removing smaller ash trees a foot or less in diameter as well as treating trees.

A state grant awarded in December 2018 has helped the process.

New Richmond

Although the pest has not been officially detected in the New Richmond city limits, the plan to prepare for the infestation has been in the works since last year.

New Richmond adopted its management plan in 2017.

In 2018, the first phase was implemented and 58 ash trees with a trunk diameter of 6 inches or less located in street boulevards were removed regardless of their health. Eleven additional ash trees were removed due to their condition rating of “poor” or “dead” as recorded in the city’s 2017 comprehensive tree inventory.

“Our removals in 2019 have been more limited based on budget, as well as the fact that EAB is lingering just on the fringe of that 15 mile mark that was set out as a measurement to kick off the next phase,” Public Works Director Jeremiah Wendt said.

He has been asked to investigate several trees on private property.

“I have had contact from a number of residents this year wondering if EAB is the reason that their tree is dying. I’ve investigated several trees that folks have called in, but haven’t found any with the telltale signs of EAB,” Wendt said.