Area-wide management approaches for year-round insecticide-resistant diamondback moth populations in Ventura County, CA

The concern over the damage by Plutella xylostella to cole crops has increased in Ventura County, and growing resistance to several modes of action has left growers with few options to control it. We are monitoring diamondback moth male adults in three areas using pheromone traps in order to explore regional and seasonal trends. Cultivar resistance was tested at 2 sites with medium and high pest pressure. Under high pest pressure, none of the 27 cultivars produced marketable heads. Two cultivars showed lower damage, but the potential yield was never higher than 10%. In the trial under medium pest pressure, 17 cultivars were tested. The yield ranged between 4% and 50%, and 5 cultivars had yields above 30%. At this site, where no insecticides were used, the number of larvae and pupae started to decrease 2 weeks after planting. Bioinsectides and Senstar were also tested at 2 sites with different pest pressures. Three of the treatments resulted in lower number of holes per plant and produced marketable yields above 50% under low pest pressure. Under high pest pressure, the bioinsecticides and Senstart treatments decreased the number of larvae and pupae, although it did not result in differences in the number of holes 4 weeks after planting. Finally, the use of insect netting was tested under very high pest pressure and was highly effective at reducing damage. Using more resistant cultivars and bioinsecticides that preserve predators and parasitoids can be effective management strategies under low to medium pest pressure.