ABSTRACT
The efficacy and dose-response, residual effect, and effect on the fecundity of neem formulations on cabbage aphid Brevicoryne brassicae applied systemically through root tissues of Brussels sprouts (Brassica oleracea), were studied in the greenhouse. Two formulations were tested; NeemAzal granules containing 7% azadirachtin (AZA), at 75, 150, 225 and 300 mg per kilogram of the substrate and a water-based formulation, NeemAzal-T (1% AZA) at 1, 1.5, 2 and 2.5 ml/kg of substrate. The efficacy of the neem formulations was dose-dependent, with the highest doses of NeemAzal granules and NeemAzal T, (300 mg and 2.5 ml/kg of substrate) respectively, having up to 0% survival of aphids by 14 days after treatment. The manufacturer’s recommended doses, NeemAzal granules at 150 mg and NeemAzal-T at 1 ml/kg of substrate, were used to evaluate the persistence and bioresidual effect of the azadirachtin on cabbage aphid over time. After treatments, plants were infested with one-day-old aphid larvae on the same day (D0), three days (D4) and eight days (D8) after treatment. There was a sharp decrease in persistence with NeemAzal-T when plants were infested 8 days after treatment, and there was no significant difference in the survival of aphids with control plants. However, there were no differences in the survival rate of cabbage aphid larvae if exposed 0, 4 or 8 days after treatment with NeemAzal granules but the survival rate was significantly lower compared to that in the control. The fecundity of aphids decreased significantly after the application of azadirachtin. In conclusion, results show high efficacy of soil-applied NeemAzal against cabbage aphid, with NeemAzal granules, which is a slow-release formulation, giving the longest period of bioactivity hence offering the longest period of protection.