Phenology and Management of Annual Bluegrass Weevil on Virginia Golf Courses

Annual bluegrass weevil (Listronotus maculicollis Kirby) (Coleoptera: Curculionidae) (ABW) is a major pest of annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northeastern United States. The asynchronous life cycle makes managing ABW difficult, putting emphasis on scouting to achieve accurate insecticide timing and acceptable control. Little is known about the biology and management of ABW in Virginia's more temperate climate. Reported cases of ABW resistance to pyrethroids (IRAC Group 3) continues to grow in the northeast, yet no pyrethroid-resistance cases have been reported in Virginia outside of the metropolitan Washington, D.C. For this thesis, I confirmed the widespread distribution of ABW across Virginia with a survey of golf course superintendents. Two golf courses in southwestern Virginia were monitored weekly during the 2019 and 2020 growing seasons to determine the seasonal biology of ABW within this region. These data suggest that overwintering ABW emerge much earlier than described in the northeast, with adult weevil activity beginning in late February or early March. I observed three complete ABW generations, with a potential fourth generation. Soil plugs from the same two golf courses were used to compare the salt floatation and Berlese-Tullgren funnel methods of larval extraction. The methods were highly correlated (R2 = 0.7856), suggesting either method is appropriate for ABW larval extraction. Bioassays conducted on adult ABW from the same two golf courses showed that field rate concentrations of the pyrethroid bifenthrin showed variable mortality ranging from 20% to 80% suggesting the presence of resistance genes in the population. A 100-fold rate of bifenthrin resulted in 100% mortality of ABW, however. Because cross-resistance has been reported among northeastern ABW populations, the common insecticide active ingredients chlorpyrifos (IRAC Group 1B: Organophosphate), trichlorfon (IRAC Group 1B: Organophosphate), λ-cyhalothrin (IRAC Group 3: Pyrethroid), α-cypermethrin (IRAC Group 3: Pyrethroid), imidacloprid (IRAC Group 4A: Neonicotinoid), and spinosad (IRAC Group 5: Spinosyn), were tested on ABW adults. In another bioassay, two organophosphates, trichlorfon and chlorpyrifos, resulted in significantly higher ABW mortality rates than all other labeled insecticides (P < 0.0001). Two other larvicides, spinosad and α-cypermethrin, also exhibited adult control, an important factor to consider for ABW management and preventing pyrethroid-resistance. These results provide valuable insight into the seasonal biology and management of ABW in Virginia and direction for further investigation into these populations.