Effectiveness of Emamectin Benzoate and Propiconazole for Protecting Picea engelmannii (Pinales: Pinaceae) from Mortality Attributed to Dendroctonus rufipennis (Coleoptera: Curculionidae) in Wyoming

Abstract

Spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), causes significant mortality of mature spruce, Picea spp. (Pinales: Pinaceae), in western North America. We evaluated the effectiveness of two formulations of bole injections of emamectin benzoate (TREE-Age G4 and TREE-Age R10; Arborjet, Inc., Woburn, MA) alone and combined with propiconazole (Propizol; Arborjet, Inc.) for protecting Engelmann spruce, Picea engelmannii Parry ex Engelm., from mortality attributed to colonization by D. rufipennis. Treatments were injected 16-19 July 2017, and levels of Pi. engelmannii mortality were determined for 2018 and 2019. Each experimental tree (n = 30, including an untreated control group) was baited with aggregation pheromone (frontalin) June-September 2018. All surviving treated Pi. engelmannii and a second untreated control group were baited June-September 2019. Both TREE-Age G4 and TREE-Age R10 significantly reduced levels of Pi. engelmannii mortality compared with the untreated control; however, protection was limited to one field season. Protection was increased to two field seasons by combining TREE-Age G4 and TREE-Age R10 with Propizol. The addition of Propizol, a triazole fungicide, likely reduced the progression of blue stain within treated Pi. engelmannii increasing tree health and resistance to D. rufipennis.