Mountain Pine Beetle A Threat to Valley Pine?

Dave Overhulser, Entomologist, Oregon Department of Forestry

In June 2005, the mountain pine beetle (Dendroctonus ponderosae) was found infesting Valley pine near Crawfordsville in Linn Co. This discovery created concern among foresters since the mountain pine beetle (MPB) is by far the most damaging bark beetle in the West. Each year millions of acres of forest, predominantly lodgepole pine, are infested and killed by this beetle. In Oregon, the MPB attacks a number of native pines including ponderosa, sugar, western white, whitebark, and lodgepole. Of its hosts, lodgepole, sugar and western white appear most susceptible to beetle infestations. Prior to its discovery near Crawfordsville, the MPB was previously collected in the Willamette Valley infesting western white pine at the USFS Dorena Genetic Resource Center in Lane Co. There were also a few unconfirmed reports of MPB attacks on Valley pine in Lane Co. during the 1980’s. The experience so far indicates that MPB activity in the Willamette Valley is a rare event.

The reason MPB attacks are very rare in the Valley is the scarcity of susceptible hosts. Ponderosa pines are not attacked by MPB unless they have a dbh >8” and are growing in overstocked stands of either pure pine or mixed species. With the proliferation of Valley pine, it is possible that enough susceptible stands will eventually exist so that MPB outbreaks could occur. However, any outbreaks in the Willamette Valley will be confined to unmanaged stands of older trees and not spread to actively managed stands.

If you are concerned about MPB infestations, there are a couple of diagnostic characteristics that can help identify attacks. One sign of MPB attacks is the presence of small pitch tubes (Fig. A) on the bark. These pitch tubes are commonly found at breast height and higher on the bole and should not be confused with the larger pitch tubes occurring within several feet of the ground produced by red turpentine beetle attacks. Removing the bark of MPB infested pines can reveal the beetle’s gallery pattern (Fig. B). Mountain pine beetle galleries are 12 – 36” in length and run parallel to the wood grain.




Last Updated 02/24/08