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For tree lovers, the emerald ash borer is no gem.

The small, iridescent green beetle has already killed more than 30 million ash trees in Michigan since it was discovered there in 2002, and it could arrive in Montana at any time.

Fred Bicha, the Billings city forester, said the beetle, which is about half an inch long when mature, is most likely to arrive in Montana lodged in imported firewood, from which it could quickly spread.

The beetle could have devastating effects on Billings and the rest of Montana. Billings city parks alone contain 1,892 green ash trees, Bicha said, and if all of them became infected and had to be cut down, it would cost nearly $500,000.

When he worked for the state, Bicha said, he did tree inventories in 11 communities stretching from Colstrip to Dillon and found that 34 percent of trees on city property were ash.

In Billings, 23 percent of the trees in city parks are green ash, and Bicha estimates they make up more than 40 percent of all trees planted on boulevards.

To deal with the threat, the Montana Urban and Community Forestry Association held a gathering in Billings last month at which city, state and private arborists met to learn how to test for the presence of the ash borer.

When the ash borer was discovered in southeastern Michigan in 2002, Bicha said, it had already been there for five years.

"We would really like to catch it a lot sooner than that," he said.

The beetle has since spread from Michigan to other states, Minnesota and Kansas being the closest to Montana.

Once a tree is infected it can't be saved. But if the beetle does show up in Montana, tree owners can use chemical treatments to ward it off. Given the great distances between cities in Montana, it might also be possible to isolate the beetle.

"If we can catch it early when it gets here, maybe we can limit it or quarantine it," Bicha said.

At the meeting in April, Cam Lay, the state entomologist with the Department of Agriculture, showed how to test a tree for the presence of the emerald ash borer.

Bicha said the technique involves removing a branch 2 to 3 inches in diameter and peeling off the bark with a draw knife. The beetle leaves a distinctive S-shaped pattern on the layer of wood just under the bark.

In the regular course of removing and pruning trees, city crews will conduct monthly tests for the ash borer, Bicha said. The beetle infects all varieties of ash, but Bicha said green ash is by far the most prevalent species in Montana, prized for its hardiness.

He also said that a mature green ash with a 20-inch diameter has an appraisal value of $5,500. Its benefits include providing shade, capturing carbon and raising property values.

Property owners should take care to diversify species when they plant trees, and if friends visit from back East, Bicha said, give them a warning:

"Tell them to leave their firewood at home. We've got enough firewood in Montana."

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I cover the city of Billings.