Assessing new chemical control options for the carrot weevil (Listronotus oregonensis) and carrot rust fly (Psila rosae) in Ontario

Carrot weevil (Listronotus oregonensis (LeConte)) and carrot rust fly (Psila rosae Fab.) are the two most important pests of carrots in Ontario, Canada. Both pests cause direct damage to carrot roots and have an international range. Recently, diazinon, the primary insecticide used to control carrot rust fly, was deregistered in Canada. It is also believed that carrot weevil is developing resistance to phosmet, which is the primary insecticide used for its control. In this study, carrot weevils were tested in the laboratory for relative susceptibility to various contact insecticides using a 1/9th scale Potter (miniature) spray tower. In 2015, 2016, several in-furrow, seed treatment and foliar insecticides were examined in field trials for carrot weevil and carrot rust fly control. In the laboratory, phosmet and clothianidin showed the greatest toxicity as contact adulticides but failed to provide effective control in field trials. In 2016 field trials, novaluron provided effective carrot weevil control and cyantraniliprole appeared to have some efficacy as both seed treatment and foliar formulations. Results from most field trials suggested a new, 2nd generation of carrot weevil is likely occurring in Ontario and requires new recommendations for effective control. Overall, minimal carrot rust fly damage was observed meaning no conclusions could be made concerning the efficacy of tested insecticides. Future research should continue to evaluate carrot rust fly control measures, examine the potential combination of seed treatment and foliar applications for carrot weevil, and assess the impact and management options for a 2nd generation of carrot weevil.