APPLICATION OF THE CABBAGE-LOOPER EQUIVALENT MODEL TO LEPIDOPTEROUS PESTS OF BRUSSELS-SPROUTS IN PRINCE-EDWARD-ISLAND

An investigation into the use of thresholds based on Cabbage Looper Eq uivalents (CLE) was conducted on Brussels sprouts, Brassica oleracea v ar. gemmifera (L.), cv. Valiant, grown in Prince Edward Island in 1991 and 1992. The CLE model was used to equate foliage consumption by lar vae of the imported cabbageworm, Pieris rapae (L.), the diamondback mo th, Plutella xylostella (L.), and the cabbage looper, Trichoplusia ni (Hubner). Management strategies included the following: (1) an untreat ed check; applications of insecticides after thresholds of (2) 1.0 CLE ; (3) 0.50 CLE; or (4) 0.25 CLE per plant were exceeded; (5) bi-weekly applications of insecticides; and (6) applications of insecticides ac cording to the grower's spray schedule. In 199 1, the imported cabbage worm was the most abundant species in the complex attacking the crop a nd high yields were obtained in all treatments. However, in 1992, the diamondback moth was the principal species and significantly reduced m arketable yields in all treatments. Use of CLE as a model for threshol d determination in the crop of Brussels sprouts underestimated the pot ential of the diamondback moth for damage and resulted in improper tim ing of applications of insecticide for adequate control of the diamond back moth.