Mountain pine beetles up the threat to region’s forests and urban trees

Gail Durham, Nevada Division of Forestry, shows bark beetle damage on a pine tree.   

Gail Durham, Nevada Division of Forestry, shows bark beetle damage on a pine tree.

Forestry officials recommend steps for storing firewood in order to avoid infestations

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CARSON CITY, Nev. – Sierra Nevada forests are approaching what could become an epidemic of pine beetle infestations. Swaths of forests in the Western U.S. and Canada have been decimated by the mountain pine beetle (Dendroctonus ponderosae), and Nevada officials are seeing more trees this year killed by the beetles in Sierra forests.

“After two years of drought, mountain pine beetles and pine engraver (Ips pini) beetles have been found in the dense stands of lodgepole pines in the Mount Rose area west of Reno,” said Pete Anderson, state forester with the Nevada Division of Forestry. “Both of these species can attack pine trees in urban areas.”

The concern is twofold, Anderson said. If 2009 is another year of below normal precipitation, the probability of the beetles killing Sierra pines may go up drastically. Wet years give trees the ability to defend against beetle attacks, while dry years—like the last two—weaken tree defenses particularly in densely forested areas.

The other problem is when firewood harvested from these areas is stored in urban communities.

“As this firewood is removed from the mountains, landowners should be aware that this wood can be harboring insects that may attack their ornamental trees,” said Gail Durham, forest health specialist with NDF. “All firewood should be stored away from any ornamental trees. The wood should be cut and split as soon as it arrives and stored under a sealed tent of thick (greater than 4 mil) black plastic sheeting. Covering the wood increases temperatures and will kill the beetles.

“Edges of the plastic should be buried into the ground at least six inches deep to prevent the beetles from emerging from under the plastic,” Durham added. “If the wood is more than a year old and dead, most of the beetles will have already flown from the wood in search of live trees to attack.”

Nevada Division of Forestry officials along with the U.S. Forest Service are closely monitoring beetle infestations and encouraging landowners to take a proactive role in protecting ornamental trees and treating infested areas.

“The purpose of thinning lodgepole pine stands while also removing beetle infested trees is to improve forest health by allowing the remaining healthy trees to become more vigorous in order to repel bark beetle attacks,” Durham said. “But by removing the wood, the woodcutter needs to be sure that they do not introduce a pest into landscapes where the beetles can damage other trees.”

Durham said that mountain pine beetles and pine engraver beetles are very small bark beetles—and the most destructive. Most urban trees are sufficiently watered and can defend against beetle attacks, but if the trees are water deficient, beetles may be able to overcome the tree’s defense by getting under the bark, breeding and laying eggs. Enough beetles under the bark will ultimately kill the tree.


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