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Cottage Grove continues fight against ash borer spread

A tiny green menace plaguing thousands of Minnesota trees is on the move.

An invasive beetle native to China, the Emerald Ash Borer has put both Ramsey and Hennepin counties in an indefinite quarantine and is slowly infesting trees around the metro. While it has yet to be discovered in Cottage Grove, the city's Parks and Recreation Department is trying to stay ahead of the bug.

In 2010, the city implemented an aggressive, $162,000-per-year treatment and prevention program aimed at assessing the city's ash trees, which make up roughly 25 percent of the city-owned tree population. Now three years into the 12-year program, Parks and Recreation Director Zac Dockter said they are on target with projected goals.

"It's hard to say if we are satisfied with the program so far," he admitted. "But, we are on pace with the goals of the program, which is to get to a point in time where the only boulevard ash trees remaining are those in our treatment plan."

Currently, about 20 percent, or 700 ash trees, have been removed and only 62 percent of the remaining ash trees are in the city's insecticide regimen. It is a large gap, Dockter said, that the city is still trying to figure out how to close.

As part of the prevention program, thousands of ash trees will be treated with injectable insecticides every three years until 2022, with the focus being on injecting 2,000 trees this year. But Dockter said dying, dead or unsightly ash trees must be removed.

To date, the city has removed nearly 700 of the city-owned ash trees and this year is implementing the next phase of the prevention program, which offers Cottage Grove residents the opportunity to voluntarily have their boulevard ash trees removed and replaced at no cost.

Residents with boulevard ash trees should expect to receive a letter stating that their tree is "slated for optional removal" in anticipation of an Emerald Ash Borer outbreak, and the option is available to choose from several different types of trees, such as varieties of oak and elm trees.

Dockter added that by voluntarily allowing their ash tree to be removed, residents help the city save on the cost of injectable insecticides and reduce the risk of financial handcuffs associated with large-scale removal operations.

"Although we are happy with our progress to date, we are still just scratching the surface in getting to a point of being comfortable," Dockter said. "This is a very financially and environmentally sound management plan that gives us the ability to manage the ash tree population before the Emerald Ash Borer manages it for is."

Quarantined, but still spreading

The Emerald Ash Borer first began tormenting trees in North America in early 2002. While it is unknown exactly how the Asian beetle first made its way to the states, experts suspect it arrived on ash wood used for stabilizing cargo in ships or crating heavy consumer products.

While the lifecycle of the beetle is short, only one to two years, they can have detrimental effects on the ash tree population. The insect begins emerging in ash trees in mid to late May with peak emergence in late June. The female Emerald Ash Borer lays eggs and within in two weeks, small larvae make their way into the bark of the tree. The borer destroys the water and nutrient conducting tissues under the bark and after two years, most of the tree canopy will be dead.

Since arriving more than a decade ago, the invasive insect has spread across the country and is now confirmed in eight states and two Canadian provinces, making it an international problem.

As recent as March 19, 2013, a Minnesota Department of Agriculture arborist discovered symptoms of the Emerald Ash Borer in trees near the intersection of Snelling Avenue and Highway 36 in Roseville in Ramsey County. The recent infestation is a clear indicator to Geir Frissoe, director of the plant protection division at the MDA, that the invasive species is continuing to spread within quarantined areas.

"We are getting much better results than other states that have implemented prevention plans and we've been able to slow the movement," Frissoe said. "But, it's still happening."

The Emerald Ash Borer can fly at least one-half mile from the tree they emerge in but can travel even farther when infected wood is transported over long distances. While the insect prefers to burrow in weak and decaying trees, they do not object to healthy ash trees. Once the invasive beetle makes its way into an ash tree, it is only a matter of time before the tree is killed. Smaller trees can die within one to two years of infestation while larger trees can be killed in three to four years.

Frissoe applauded the city's prevention plan to diversify the tree population through the voluntary removal and replacement program, and said preparing for the Emerald Ash Borer by treating healthy trees is yet another step in the right direction.

"I think there is a good chance Cottage Grove can evade an infestation if preventative measures continue to be taken," Frissoe said. "Unfortunately, the ash tree is a very good urban tree and adapts well to many city stresses. But, I think speaking long-term, communities such as Cottage Grove need to be looking at diversifying tree species. Overall, I think the Twin Cities has done a good job trying to prepare for the Emerald Ash Borer."