Evaluation of biological methods of pest control for Chinese kale in a vegetable production system

Field trial was undertaken to evaluate the comparative efficacy of different biological control methods against major cruciferous insect pests on Chinese kale (Brassica alboglabra, Bailey). The treatments selected for study were the commercial preparation of neem extract (Azadirecta indica, Juss.) and Bt (Bacillus thuringiensis, Berl.) both at two different concentrations i.e 100 cc/20 lit of water and 50 cc/20 lit of water, three repellent crops viz. citronella grass (Cymbopogon wintereanus), sweet basil (Orimum basilium, L.) and pepper mint (Mentha viridis), a common chemical insecticide (atabron) and the control. The major pests monitored in the field were diamondback moth (Plutella xylostella, L.), cutworm (Spodoptera litura, F.), cabbage webworm (Hellula undalis, F.), flea beetle (Phylotetra spp.) and cabbage semilooper (Trichoplusia ni, Hb.). Among them DBM was found to be most dominant one. The yield of Chinese kale obtained from Bt and neem extract (both at higher concentration) were higher than from atabron. Among the repellent treatments, the highest yield was harvested from the mint plots, which was also higher than from chemical treatment. Both Bt and neem extract at the lower concentration gave lower yield than atabron, but statistically not different at 5 % level. Similarly, the biological treatments were found equally or even more (Bt at higher concentration) efficient in killing or driving away the pests in or from the vegetable beds than the chemical treatment. But unlike the chemical spray, the bio-sprays did not show immidiate effect on the pests larvae (i.e after 36 hrs of spray), but later (i.e when counted after 5 days of spray), they have shown a better efficacy than chemical spray causing higher rate of larval mortality. Among the three repellent treatments, lowest number of DBM larvae were recorded from basil plots, followed by mint and citronella. The selected biological methods in the study were found to be more economical to practice than spraying the chemical insecticide. The dominance analysis has confirmed that Bt and neem spray at higher concentration and mint are the dominant methods which give relatively higher net revenue at lower variable costs.