Evaluations of emamectin benzoate and propiconazole for protecting individual Pinus contorta from mortality attributed to colonization by Dendroctonus ponderosae and associated fungi

Abstract

Protection of conifers from bark beetle colonization typically involves applications of liquid formulations of contact insecticides to the tree bole. An evaluation was made of the efficacy of bole injections of emamectin benzoate alone and combined with the fungicide propiconazole for protecting individual lodgepole pine, Pinus contorta Dougl. ex Loud., from mortality attributed to colonization by mountain pine beetle, Dendroctonus ponderosae Hopkins, and progression of associated blue stain fungi. Injections of emamectin benzoate applied in mid-June did not provide adequate levels of tree protection; however, injections of emamectin benzoate + propiconazole applied at the same time were effective for two field seasons. Injections of emamectin benzoate and emamectin benzoate + propiconazole in mid-September provided tree protection the following field season, but unfortunately efficacy could not be determined during a second field season owing to insufficient levels of tree mortality observed in the untreated control, indicative of low D. ponderosae populations. Previous evaluations of emamectin benzoate for protecting P. contorta from mortality attributed to D. ponderosae have failed to demonstrate efficacy, which was later attributed to inadequate distribution of emamectin benzoate following injections applied several weeks before D. ponderosae colonization. The present data indicate that injections of emamectin benzoate applied in late summer or early fall will provide adequate levels of tree protection the following summer, and that, when emamectin benzoate is combined with propiconazole, tree protection is afforded the year that injections are implemented.