Biology of Mint Root Borer (Lepidoptera: Crambidae) and Control Options on California Peppermint

Mint root borer, Fumibotys fumalis (Guenee), larvae cause damage to peppermint by feeding on rhizomes belowground. This species can cause significant economic damage and occurs throughout all peppermint-growing regions in Washington, Oregon, Idaho, and California. Until 2009, managing economic populations was limited to fall or spring tilling, and postharvest application of the organophosphate insecticide, Lorsban. The recent registration in California of the reduced risk insecticides chlorantraniliprole, indoxacarb, methoxyfenozide, and spinetoram on peppermint potentially improves management tactics by including preharvest applications. A degree-day model, available through the Oregon State University, Integrated Plant Protection Center (OSU IPPC), provides information that could be used for applying preharvest insecticides targeting vulnerable life stages. In 2010 and 2011, large delta sticky traps baited with mint root borer sex pheromone were placed in commercial peppermint fields in Shasta and Siskiyou counties and used to validate the OSU IPPC model under California conditions. Moth capture data indicated that the OSU IPPC model did not provide a reliable prediction of emergence, peak flight, and 90% flight. In 2010, observed peak flight varied 10-25 days earlier than predicted by the OSU IPPC model. Observed 90% flight occurred ∼2 weeks earlier than predicted in Shasta County and nearly 1 month earlier than predicted in Siskiyou County during 2010 and 2011, respectively.