Insecticide dip treatments to prevent walnut twig beetle colonization of black walnut logs
The health, sustainability, and commercial viability of eastern black walnut (Juglans nigra) are currently under threat from thousand cankers disease. The disease is caused by an invasive bark beetle species, the walnut twig beetle (Pityophthorus juglandis), and its associated fungal pathogen (Geosmithia morbida). Range expansion of the beetle and pathogen has likely been facilitated by transport of infested walnut forest products. Preventing colonization of these products is crucial to limiting further spread of thousand cankers disease. This study evaluated three insecticides for their ability to induce walnut twig beetle mortality and prevent colonization of black walnut bolts, 3 to 5 cm in diameter, after dip treatment applications. Treatments included 0.003 percent azadirachtin, 15 percent disodium octaborate tetrahydrate (DOT), 0.5 percent permethrin, and water in Trial 1, and 0.013 percent azadirachtin, 30 percent DOT, 0.5 percent permethrin, and water in Trial 2. A total of 40 beetles, 4 beetles per sample, were exposed to treated samples and observed for 120 hours in each trial. Permethrin was the only treatment to achieve 100 percent mortality and prevent all colonization activity. The 30 percent DOT treatment increased mortality compared with the control; however, it did not reduce the mean number of attacks or mean gallery length. Azadirachtin was not effective at either concentration. Results suggest that insecticide dip treatments can prevent walnut twig beetles from colonizing cut black walnut logs. Treatments could be used in conjunction with phytosanitation to help prevent further spread of thousand cankers disease while allowing for the continued transport of bark-on walnut forest products.