Assessment of the walnut twig beetle’s (Pityophthorus juglandis) ability to colonize treated black walnut (Juglans nigra) wood

Thousand cankers disease (TCD), caused by the walnut twig beetle (Pityophthorus juglandis) and the pathogen Geosmithia morbida, is an invasive disease complex causing walnut (Juglans) declines across the west and in several states in the eastern US.  First discovered in the black walnut (Juglans nigra) native range in 2010, TCD continues to spread and threaten a valuable hardwood resource. This study sought to assess the efficacy of phytosanitation methods in preventing walnut twig beetle (WTB) colonization post-treatment.  Bolts of un-infested black walnut were cut and treated.  Treatments included steam heated, fumigated, kiln dried lumber with bark on, kiln dried lumber with bark removed, and a no treatment control.  Bolts were baited with WTB lures and hung for 30 days in infested walnut trees in Knoxville, TN.  Colonization was assessed by recording emergence and mapping WTB gallery lengths.  All treatments significantly reduced the mean beetle concentration compared to the control, however, WTB successfully colonized the heat and fumigated treatments.  Beetles were also recovered from several of the kiln dried, bark on lumber samples.  These results suggest further protection post phytosanitation treatment may be required in order to prevent further spread of the insect and pathogen.