Microsclerotial Granular Formulation of the Entomopathogenic Fungus Metarhizium brunneum and Its Combinations With Hydrogel and Imidacloprid Against the Annual Bluegrass Weevil (Coleoptera: Curculionidae)

Abstract

We determined the potential of the entomopathogenic fungus Metarhizium brunneum Petch (Hypocreales: Clavicipitaceae) F52 strain, and of a microsclerotial formulation, for the control of the annual bluegrass weevil, Listronotus maculicollis Kirby, which is a major pest of golf course turf in eastern North America with widespread insecticide resistance. Under laboratory conditions in Petri dishes with moist sand, the microsclerotia (23-46 kg granules/ha) caused high rates of mortality (85-100%) and infection (67-80%) in annual bluegrass weevil adults, but these levels did not occur until after 9 d at constant 26°C and 12-15 d at 14 h at 23°C and 10 h at 17°C. Production of viable conidia was marginally higher at the higher temperature regime (7.3 vs. 5.2 × 109 per gram of granules). Application of microsclerotia did not provide significant control and infection of adults in pots with grass in the greenhouse. In field trials targeting spring generation larvae, microsclerotia application (50-100 kg granules/ha) was ineffective, and coapplication of hydrogel to stabilize soil moisture did not increase larval control. A liquid M. brunneum F52 conidial formulation (4.75-9.5 × 1013 colony forming units/ha) provided up to 51% control. Combinations of M. brunneum F52 with the neonicotinoid insecticide imidacloprid provided additive control with up to 70% control with the conidial formulation. Field efficacy was probably limited by suboptimal temperatures for the fungus, and future tests need to examine whether higher control rates can be achieved in applications targeting the summer generation larvae.

Keywords: microsclerotia; biological control; hydrogel; imidacloprid; turfgrass.