Effective Use Of Bacillus Thuringiensis Berliner Subsp. Kurstaki For Control Of Diamondback Moth (Plutella Xylostella) (L .) (Lepidoptera: Plutellidae) On Cabbage

Two field experiments were carried out at W eija Irrigation Company (Ghana), from February to November 1995 on the effective use of Bacillus thuringiensis Berliner subsp. kurstaki (Dipel 2X) against the diamondback moth Plutella xylostella on cabbage (Brassica oleraceu var. capitata (L.). In the first experiment, different concentrations (0.25 g/1, 0.5 g/1, 1.0 g/1 and 2.0 g/1) of Bacillus thuringiensis subsp. kurstaki (B.t.) were applied at weekly and fortnightly intervals on cabbage plots. In all the treatments, B.t applied at weekly intervals was more effective in controlling Plutella xylostella larvae than those sprayed every fortnight. The highest harvestable heads of 92.3% was recorded on plots sprayed with 1.0 g/1 at weekly intervals. On the control plots only 32.9% of the heads were harvested. Yellow sticky traps used to sample adult diamondback moth and other insects were found to be effective. In all 109 different insect species belonging to 8 orders were collected. In the second experiment 1.0 g/1 of Bacillus thuringiensis was applied weekly on cabbage at different stages of the cabbage growth. Cabbage plots treated at 3 and 5 weeks after transplanting did not show any significant difference in yield compared to cabbages that received treatment a week after transplanting. Depending on consumer preference cabbages that were not treated after 5 weeks resulted in yield reduction of about 70% where cabbages with minor damages are accepted and over 95% reduction for premium cabbage. A weekly spray of Dipel 2X at 1.0 g/1, commencing not later than 5 weeks after transplanting is therefore recommended. It is also suggested that, yellow sticky traps could be used together with Bacillus thuringiensis in integrated management of diamondback moth, since B.t. does not affect adult Plutella .xylostella.