Control of diamondback moth plutellaxylostella(l) (lepidoptera: yponomeutidae) in cabbage using neem-based pesticides in Kenya
Experiments were carried out in the screenhouse at KARI, Thika (1dec 09S and 37dec 04E) in Central Province of Kenya, between October 1996 and July 1997. These were aimed at determining the effective rates of application of neem Kernel cake powder (NKCP) and neem Kernel cake powder water extract (NKCP-WE) for controlling diamonback month (DBM). NKCP was applied as soil amendment in the nursery bed and in the transplanting hole, while NKCP-WE was applied as foliar spray in a Rondomized Complete Block design (RCBD). Foliar application was later compared with a standard biopesticide Dipel 2x. The parameters evaluated included the effect of neem on seed germination, plant growth, crop yield, larval growth and development, and larval damage to the plant. Results showed that nursery bed amendment 0g, 10g, 30g, 40g, and 50g NKCP/0.12m2) improved plant growth, an observation attributed to high nitrogen content of the powder, although the effect was not significant (P>0.05). Phytotoxicity was noted in 40g and 50g NKCP treatments. Larval growth and development, and plant damage in 10g, 20g and 30g treatments did not differ significantly (P>0.05) from control. Application in the transplanting hole (0,1.75g, 3.5g and 7g NKCP per plant) showed maximum effect 2 weeks after treatment. However only 3.5g and 7g NKCP treatments significantly (P<0.05) reduced larva growth and feeding. The effect lasted for about two weeks. This mode of application is however not recommended due to the large amount of powder required. Foliar application of NKCEP-WE (0g, 12.5g/1,25g/1, and 50g.1) was very effective in controlling the DBM larvae. All the concentrations were larvicidal and significantly (P<0.05) reduced larval damage to the plants. 12.5g/1 was effected for one week while the efficacy of 25g/1 lasted for two weeks. Comparison of Dipel 2x and neem (25g/1 and 50g//1) treatments showed that plants treated with the former had lower DBM population and less damage than those treated with the latter, although differences were not significant (P=0.05). However, neem treated plants had significantly higher yields than either Dipel 2x treated or the control plants. This yield difference could have been as a result of aphid infestation since both Dipel 2x treated plants and the control plants were heavily infested by aphids. Field trials would be necessary to confirm these results.
- MST-Zoological Sciences