Cooperative Extension Service Communications and Technology Department 3354 1000 E. University Ave. Laramie, WY 82071 (307) 766-6342 • fax (307) 766-3998 • www.uwyo.edu

 

For Immediate Release

Story Contacts:

Scott Schell: (307) 766-2508

Les Koch: (307) 777-5495

 

Contact: Steven L. Miller, Senior Editor

Phone: (307) 766-6342

E-mail: slmiller@uwyo.edu

Archived News Site www.uwyo.edu/agadmin/news/news.htm

 

Date: Aug. 21, 2006

 

Harvesting pine beetle-infested firewood brings unwanted pests to town

            Harvesting firewood from trees killed by pests could bring those pests to town.

            Years of drought and bark beetle infestations have left many standing dead trees in firewood-gathering areas, said Scott Schell, a research scientist and assistance extension entomologist in the Department of Renewable Resources at the University of Wyoming, and Les Koch, forest health specialist with the Wyoming State Forestry Division,

            If those trees still have red or yellowed needles, the next generation of the beetles that killed them may still be under the bark, they said. Beetles that emerge from under the bark can attack susceptible species of trees as far away as a mile from the firewood pile.

            The most common tree-killing beetle in Wyoming transported with firewood is the mountain pine beetle (Dendroctonus ponderosae), which attacks lodgepole, ponderosa, limber and white bark pine, the two stated.  The mountain pine beetle will attack and kill as many as 13 different species of pine trees, many of which can be found in towns.  The beetles carry a fungus that clogs the vascular tissues carrying nutrients to the needles, gradually killing the tree.

            The beetle has a one-year lifecycle, and new adults emerge from infested trees by chewing their way out through the bark, usually starting in July.  These emergence holes make the bark look like it was shot with a shotgun. 

            The number of beetles produced by one mountain pine beetle-infested tree is estimated to be enough to infest two more trees of similar size. 

            The emerged adult female beetles fly away in search of trees of suitable size (8 inches or more in diameter are preferred) and species to bore through the bark to create a characteristically shaped gallery or chamber in the tree’s phloem. 

            The phloem layer contains cells that produce new tissue responsible for increased girth.  The beetles lay eggs in the gallery, and the trees try to defeat the attack by producing enough pitch to force the beetle back out.  These gobs of resinous sap and chewed-up bark are called pitch tubes.  They can be seen in the tree trunk from near the ground to 30 feet up on big trees. 

            Dead beetles can sometimes be found embedded in the pitch tubes if the tree wins the battle.  The more beetles that attack a tree, the more likely they will succeed.  Trees stressed by drought, overcrowding or physical injury are more likely to succumb. 

            Even healthy, watered trees in town can be successfully attacked if bark beetles are numerous. 

            Schell and Koch said Engelmann spruce and Douglas fir trees harvested for firewood have different, yet just as harmful, species of beetles that attack them and can pose a threat to ornamental trees in towns.  These trees don’t produce pitch tubes in response to a bark beetle attack.  Sawdust pushed from the entry holes and flakes of bark removed by woodpeckers seeking an easy meal signal trees infested with other species of bark beetles.

            The two advise harvesting firewood only from trees dead long enough that all needles have fallen and emergence holes are present in the bark. When trees have decayed to that stage, the insect species living under the remaining bark or in the wood are not threats to surrounding, living trees, they said. 

            Stack firewood on top of other logs or pallets to assist drying.  Long-horned or metallic wood-boring beetles may occasionally infest firewood.  These insects are generally beneficial since they construct large galleries in the wood that aids airflow throughout the pile and shortens drying time.  They typically do not attack surrounding healthy conifer trees. 

            If there is question as to the activity or status of a dead tree’s infestation, pick another tree without needles and harvest the questionable one next year to keep urban pine trees safe. 

            On the Web: http://www.fs.fed.us/rm/landscapes/Solutions/Pinebeetle

http://www.uwyo.edu/UWRENEWABLE/

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