Evaluation of pheromone trapping for prediction of diamondback moth infestations in vegetable brassicas

Abstract

The use of pheromone traps was investigated as a monitoring tool to forewarn crop scouts of risk periods when diamondback moth (DBM; Plutella xylostella) larval numbers in crops are likely to increase to damaging levels We monitored traps at five brassica planting sites for 8 months and also counted numbers of DBM larvae on 50100 plants at each site Crops were scouted weekly and insecticide application decisions were made using the Crop amp; Food Research IPM programme Results showed that increases in moth trap catches predicted increases in larval infestations in three of four commercial crops in spring by 23 weeks and gave 2 weeks warning in four of five summer crops An epizootic of Zoophthora radicans caused a rapid decline in larval populations in mid to late January at all sites In these trials use of the IPM action thresholds led to a 75 reduction in insecticide use on vegetable brassica crops Overall pheromone traps were of limited value except in early spring because crops needed to be scouted regularly for other pests