Alternative timing of carbaryl treatments for protecting lodgepole pine from mortality attributed to mountain pine beetle

•We evaluate the efficacy of spring and fall treatments of carbaryl for protecting lodgepole pine from mountain pine beetle.•Both treatments provided two field seasons of protection.•Results from a third field season were inconclusive due to insufficient beetle pressure.

Carbaryl is regarded among the most effective, economically viable, and ecologically-compatible insecticides available for protecting conifers from bark beetle attack in the western United States. Treatments are typically applied in spring prior to initiation of bark beetle flight for that year. We evaluated the efficacy of spring and fall applications for protecting individual lodgepole pine, Pinus contorta Dougl. ex Loud, from mortality attributed to mountain pine beetle, Dendroctonus ponderosae Hopkins, the most notable forest insect pest in western North America. Both spring and fall treatments of 2.0% a.i. carbaryl (Sevin® SL) were efficacious for two field seasons, while results from a third field season were inconclusive due to insufficient beetle pressure. We discuss the implications of these and other results to the management of D. ponderosae.