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Protecting forests: Koch sees emerald ash borer as next big challenge

by Wyoming Livestock Roundup

Casper – The mountain pine beetle epidemic has subsided across much of Wyoming, but Wyoming State Forestry’s Forest Health Specialist Les Koch said the state has another challenge on the horizon.

“Emerald ash borer is going to be important to Wyoming,” Koch said during the Wyoming Weed Management Rendezvous on Jan. 21. “We have not seen the bug in Wyoming yet, but it was detected in 2013 in Boulder, Colo. It has not been detected beyond the corporate limits of Boulder County yet.”

Regardless, the prominence of ash trees in the state of Wyoming means the bug could have significant impacts if it reaches Wyoming.

Impacting trees

“Green ash is native to the eastern side of the state, and every community in Wyoming has Green ash trees,” Koch explained. “It is widely planted in the state.”

Emerald ash borer invades trees similarly to how pine beetles kill pine trees.

“Literature tells us that adults emerge in mid- to late-May and peak in June,” he said, adding that until the bug appears in Wyoming, its exact habits in our environment will be unknown. “Everything is different in Wyoming.”

In outbreaks across the country, Koch said that emerald ash borer travels throughout contiguous stands of trees. The larvae of the beetle feed on the inner bark of the ash, disrupting the tree’s ability to transport both water and nutrients, subsequently killing the tree.

According to Koch, trees infected with emerald ash borer often exhibit sparse leaves and branches in the upper part of the tree during the growth season. Vertical splits in the bark are also common when dealing with emerald ash borer.

“New sprouts on the lower trunk and in the lower branches are another sign,” Koch said. “If we see a sparse crown as well as branches on the lower trunk, it might be wise to see what is causing the problem.”

Beetle lifecycle

Similarl to pine beetle, the emerald ash borer larvae winter under the bark of the tree.

“The segments of the larvae look like small bells,” Koch said. “It is pretty easy to identify.”

In addition, indicates that woodpeckers tend to like to eat the larvae, and heavy woodpecker damage may be a sign of infestation.

As the larvae emerge from the tree as adult beetles, they leave “D” shaped exit holes in the bark.

The adult beetle is metallic green and about one-half inch long.

Similar bug

Another bug, the ash bark beetle, may be confused for the emerald ash borer, but Koch explained the bark beetle is native to Wyoming, which makes it less of a concern.

In differentiating the bark beetle from the emerald ash borer, Koch explained that the bark beetle bores holes that are perpendicular to the main gallery of the tree, rather than parallel.

Green ash bark beetles also make small, pinhead-sized holes in the tree.

“If we see perpendicular tunnels and breathing holes, we do not have emerald ash borer,” he said.

Spreading pest

Wyoming is fortunate in that the large distances between cities mean that emerald ash borer would likely be unable to fly between communities to spread.

“How would it likely spread? Firewood,” Koch said. “If we have firewood with the insect underneath, we are going to have problems.”

He also noted that in Michigan, where the outbreak was first detected in 2002, emerald ash borer made an immense impact because of firewood movement.

Koch recommended that people seeking firewood should cut it in local areas.

“Anyone who does cut firewood should get it from a local forest so the native insects are present,” he said. “Firewood that is cut from national forest system land with a permit or that is transported should have the needles removed and make sure the bark has fallen off.”

If the bark is still intact, Koch recommended removing bark to make sure there are no larvae present.

“The insects can survive even in one-foot bolts of stacked firewood,” he added. “They will find the next available pine tree – whether that is on our property, the neighbor’s property or in a city park.”

Other recommendations

Koch added that, while emerald ash borer may become a threat, he wouldn’t go so far as to recommend against planting ash trees.

“I recommend the 10, 20, 30 rule,” he explained. “If we are going to plant Green ash trees, make sure no more than 10 percent of a stand is Green ash.”

He further adds that no more than 20 percent of the ash species should be planted, and no more than 30 percent of the same family of tree should be planted in a stand.

“We shouldn’t plant more than 10 percent of a species, 20 percent of a genus or 30 percent of one family in a stand,” Koch said. “We can still plant ash, but we need to diversify and plant other trees as well.”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

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