A comparison of three methods of monitoring the carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae)

The carrot weevil, Listronotus oregonensis (LeConte), was monitored at 11 research or commercial carrot plantings at Holland Marsh, Kettleby, Ontario, using three methods, i.e. wooden plate (Boivin) traps to capture adults, carrot root sections placed in the soil to detect oviposition, and recording the numbers of adults present on carrot root sections. All three methods provided similar records of the seasonal pattern of adult activity. At most sites, thresholds used to determine the need for insecticide applications were reached or exceeded soon after the beginning of monitoring. There were significant linear relationships among the seasonal activity parameters generated by the three methods and between those parameters and percentage injury at harvest. Control programs that would have resulted from the use of each method are discussed.