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Tiny green menace threatens city trees

Cottage Grove officials have begun discussions on how to protect the almost 4,000 ash trees in public right-of-way and city parks from the destructive emerald ash borer. The invasive beetle, which began its spread in Michigan, is now killing ash trees as close as St. Paul.

It's green. It's mean. And it's heading south Washington County's way.

The emerald ash borer, an invasive Asian beetle that has killed millions of ash trees from Virginia to Wisconsin, is bearing down on the Twin Cities, threatening to devastate the popular boulevard tree that lines streets and shades back yards across the Midwest.

Last Wednesday, Cottage Grove City Council members listened to what mayor Myron Bailey called the "sobering news" that the little green menace is knocking at the city's door -- and that could mean big problems for Cottage Grove's sizable ash tree population.

"It's kind of a scary situation (that) we're looking at," said Steve Bowe, the city's forester.

First detected in Michigan in 2002, the bright green beetle has spread across the Midwest and cropped up in places like Virginia, Maryland and Kentucky. Officials as close as St. Paul are struggling with infestation.

Now, Cottage Grove officials are bracing for the bug, scrambling to figure out a way to save the 3,900 ash trees lining the city's streets and dotting its parks and public land.

"Think of the asset value," city administrator Ryan Schroeder said. "If we lose 3,900 ash trees ... what do you think it would take to replace those? It would take 20 years of growth of some other trees."

The three-quarter-inch bugs have no natural predators, Bowe said, and are extremely lethal to North America's defenseless population of ash trees. They mate by the thousands, then burrow under a tree's bark and cut off the flow of moisture and nutrients between roots and limbs.

'Get ahead of the ballgame'

Bowe said the emerald ash borer's spread to Cottage Grove is inevitable. But he also said the city still has time to prevent a repeat of scenes playing out in places like suburban Detroit, where whole city blocks have been left virtually treeless after the bug's invasion.

But, no solution is cheap. After talking with officials in St. Paul, Rochester and La Crosse, Wis., -- three cities already dealing with the emerald ash borer scourge -- Bowe recommended a 12-year plan to combat the ash borers that includes:

n The removal of 39 percent of the city's ash trees in public right-of-ways -- those deemed already unhealthy and most likely to succumb to the invasive beetle.

n The replanting of new, non-ash varieties in their place.

n And the treatment of the remaining ash trees every three years for the next 12 years with a chemical Bowe says is nearly 99 percent effective in staving off infestation.

Removal of some trees is needed, the forester said, to "reduce overhead" -- city staff won't be able to handle the burden of thousands of ash trees dying in succession.

The plan, Bowe estimated, would cost the city $1.95 million over 12 years, or $162,000 per year. It's roughly half the price tag the city would shoulder if it chooses instead to simply cut down ash trees as they die and plant new boulevard trees in their place.

"If we get ahead of the ballgame," Bowe said, "you know, we might be looking all right as long as we take some right steps."

Schroeder said officials would tackle the emerald ash borer issue during next month's budget discussions. The city, he said, needs "to figure out what we can reasonably afford in the next couple years.

Bowe said the first step is to place a series of traps near Cottage Grove's northern border that will help officials detect the presence of the beetles. The trap uses an oil to attract bugs already in the area, which then adhere to a bright purple box.

Cottage Grove Public Works is already receiving calls from concerned homeowners who have spotted green bugs on their trees, officials say.

Homeowners will be responsible for the care of ash trees in their yards, Schroeder said, but city officials also plan to provide residents with information and recommendations on treatment options.

"We need to take this and run with it," Bowe said, "before it catches up to us."