Staining, in the shape of a many-pointed star, is evident in the cut ends of silver maple logs. / Photo Credit: Chris Firgens, Oconto County Forest
By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665
Columbian timber beetle (Corthylus columbianus) is an ambrosia beetle native to the eastern United States.
In Wisconsin, we have had reports of Columbian Timber Beetle (CTB) attacking silver maple in the northeastern and lakeshore areas of the state, dating back to the early 1990s. The insects have caused significant staining from repeated attacks. In southern Wisconsin, CTB can attack oaks to a lesser degree, including bur, northern red and white oak.
A new Wisconsin Department of Natural Resources Forest Health fact sheet on Columbian timber beetle is now available. It offers more information on the impact on silver maple, how to survey for damage and what to expect at the time of harvest.
A map of Wisconsin counties in which Columbian timber beetle has been found causing staining in maple. / Graphic Credit: Linda Williams, Wisconsin DNR
These beetles bore tiny holes directly into the tree. Attack by CTB does not kill the tree or cause decline, but it does cause extensive staining that may go unnoticed until the time of harvest. Beetles can bore into the trunk or larger limbs from ground level up to at least 20 feet. Staining, once introduced, does not disappear over time, so repeated yearly attacks can cause staining to accumulate within the tree.
CTB galleries and the associated staining do not cause structural defects in wood. Still, stained wood may be valued significantly less than clear wood unless the seller is able to find a specialty market for it. Lumber with this staining defect is sometimes called flagworm maple, ambrosia maple, pinhole maple or wormy maple.
A cross-section of a silver maple log showing how beetles have bored into the tree and introduced staining around the holes. / Photo Credit: Chris Firgens, Oconto County Forest
Unfinished boards show staining from Columbian timber beetle attack. / Photo Credit: Linda Williams, Wisconsin DNR