AN ACTION THRESHOLD FOR CONTROL OF LEPIDOPTEROUS PESTS OF CABBAGE IN PRINCE EDWARD ISLAND

Abstract Action thresholds for imported cabbageworm, Pieris rapae (L.), diamondback moth, Plutella xylostella (L.), and cabbage looper, Trichoplusia ni (Hübner), were evaluated on two cultivars of cabbage, Brassica oleracea var. capitata (L.), in Prince Edward Island. Thresholds were tested on plots of mid-season cabbage, cv. Minicole, and late-season cabbage, cv. Lennox, both grown for fresh market in 1991 and 1992. Management of larval populations at a threshold of 0.25 Cabbage Looper Equivalents (CLE) per plant resulted in yields equal to those obtained with bi-weekly applications or grower treatments. Higher thresholds of 0.50 and 1.0 CLE per plant were not as useful and did’ not consistently result in yields greater than untreated plots. Use of the threshold of 0.25 CLE per plant reduced the number of applications of insecticides by 30% compared with spraying insecticide at bi-weekly intervals from heading to harvest, and 43% compared with management by the grower without regard to insect populations or growth stage of the crop.