Implementing of an IPM programme for vegetable brassicas in New Zealand

In New Zealand, increasing levels of resistance in diamondback moth (DBM) to recommended synthetic pyrethroid and organophosphate insecticides were monitored for five years in vegetable Brassica crops until in 1997 they were associated with control failures in three regions. Subsequently, Crop & Food Research initiated a two-year IPM implementation programme with financial assistance from government and industry, including agrochemical companies. The IPM programme emphasizes the use of a reduced spray programme developed in the early 1990s based on a crop scouting system using presence/absence per plant of the major pests and a proven action threshold for cabbage. Further research has reconfirmed this cabbage action threshold, and broccoli and cauliflower action thresholds have been developed. The implementation phase involved training scouts and crop managers in insect identification and crop scouting techniques, and incorporated an accreditation system for trainees and a crop management recording system to document insecticide use in the IPM crops. Demonstration sites in three of the main Brassica growing regions were used for grower field days and to compare IPM practices with conventional pest management. Levels of resistance in DBM to the commonly used groups of insecticides were monitored and resistance levels were compared within a region as well as between regions. The IPM programme also recommends an insecticide resistance management rotation strategy with different chemical groups assigned to two different seasonal windows as well as the preferential use of selective insecticides to preserve natural enemies. An independent survey in November 2001 reported that 80% of growers in the main Brassica-growing region were using IPM and 96% were using crop scouting. Crop management records from IPM crops show an average saving of at least 50% in insecticide use compared with conventional crops.