Optimum timing of insecticide applications against diamondback moth Plutella xylostella in cole crops using threshold catches in sex pheromone traps

Field trials were conducted in cabbage (Brassica oleracea var capitata), ca uliflower (B oleracea var botrytis) and knol khol (B oleracea gongylodes) c rops at two different locations in Karnataka State (India) to optimize the timing of insecticide applications to control the diamondback moth, Plutell a xylostella, using sex pheromone traps. Our results indicate that applicat ions of cartap hydrochloride as insecticide during a 12-24h period after th e pheromone traps had caught on average 8, 12 and 16 males per trap per nig ht in cabbage, cauliflower and knol khol, respectively, were significantly more effective than regular insecticide sprays at 7, 9, 12 or 15 days after transplantation. This was demonstrated by estimation of the mean number of eggs and larvae per plant, the percentage of holes produced, as well as th e marketable yield of the three crops at each location. A good correlation between the immature stages, infestation level, the estimated crop yield an d the number of moths caught in pheromone traps was also found, indicating the usefulness of pheromone-based monitoring traps to predict population de nsities of the pest. (C) 2001 Society of Chemical industry.