Intercropping and Modification of Irrigation Method for the Control of Diamondback Moth

Monitoring of diamondback moth (Plutella xylostella L) population on cabbage and Chinese cabbage over the past eight years has indicated that heavy rains from June to September limit the population of the insect. Therefore, during the dry period when diamondback moth is a serious pest, water was applied by sprinkler system placed 1.5 m over the cabbage crop rather than by traditional furrow irrigation. Sprinkler irrigation applied for five minutes at dusk on alternate days over the first three to four weeks, and every day thereafter, significantly reduced the diamondback moth infestation and increased the yield over drip irrigation check plots which received an equal amount of water. The physical disruption of flying activity, oviposition, and to some extent wash-off of larvae and adults were presumably the major causes of the observed effects. In an intercropping study, cabbage was planted between two rows of each of 54 selected crops. Intercropping with tomato, dill, garlic, safflower, oat, and barley reduced diamondback moth damage to cabbage. Laboratory study indicated that application of tomato leaf extract to cabbage significantly reduced diamondback moth oviposition on treated surfaces.