Early Warning System for the Carrot Weevil (Coleoptera: Curculionidae) and Its Evaluation in Commercial Carrots in Ontario

Abstract

The carrot weevil (CW), Listronotus oregonensts (LeConte), was monitored during the active period of overwintered adults (early May–early July) in commercial carrot fields and experimental plots in the Holland Marsh, Ontario from 1980 to 1983. Carrot root sections were placed in soil between carrot rows and examined at 3- to 4-day intervals, to detect oviposition cavities. The method provided a seasonal record of CW activity that was more precise than traps for adults. It also provided an early warning of the need for insecticide application, since peak activity in carrot root sections generally occurred before new crop carrots were susceptible to attack. A tentative action threshold of 0.3 cavities per section per day, or 0.5 cavities per section per day if <50% of carrot root sections are infested, is suggested. Satisfactory control of CW was achieved in commercial fields where insecticide application was recommended based on monitoring, and where two sprays of phosmet (1.1 kg [AI]/ha) were applied.