Integrated Management of the Diamondback moth (Plutella xylostella L.) on cabbage (Brassica oleracea var. capitata) in Zimbabwe

Abstract

The diamondback moth (Plutella xylostella L.) (DBM), (Lepidoptera: Plutellidae), is a major pest of brassicas worldwide and is estimated to cost US$ 1 billion in direct losses and control costs. Field studies were conducted at Africa University to evaluate the impact of intercropping and insecticides on DBM population density in cabbage (Brassica oleracea var. capitata) cultivar Drumhead. Two trials were conducted and each had five treatments in a Randomized Complete Block Design (RCBD). Cabbage seedlings were raised in a greenhouse and transplanted into field plots on 29 September 2010. Compound S (7-21-8 and 7.5 % S) was applied as a basal fertilizer at a rate of 300 kg/ha. At 40 days after transplanting, a top dressing of Ammonium Nitrate (AN) was applied at a rate of 100 kg/ha. Cultural practices such as weed control and sprinkler irrigation were carried out as when necessary. For the intercropping trial cabbage was intercropped with Brassica juncea, Tomato (Lycopersicon esculentum Mill.) and Cleome gynandra, and B. juncea was sown as a sole crop. Sole cabbage was used as the control. For the insecticide trial, the insecticides used were Match 5 EC (lufenuron), Malathion 50 EC (malathion), Decis 2.5 EC (deltamethrin) and Malathion 25 WP (malathion). Unsprayed cabbage was used as the control. Results of the study demonstrated the impact of intercropping cabbage with tomatoes in managing DBM population below the economic injury level of 1.0 larva per plant. The mean of DBM population density varied from 0.03 to 2.42 small larvae per plant and 0.09 to 2.06 large larvae per plant. The lowest DBM density was on B. juncea as a sole crop with an average of small and large larvae of 0.06 larvae per plant. The average DBM population density on cabbage intercropped with tomato was 0.94 small larvae per plant and 0.97 large larvae per plant. The density of larvae parasitized by Cotesia plutellae was significantly higher (P<0.05) in cabbage intercropped with tomato with a mean of 0.60 parasitized larvae followed by cabbage intercropped with B. juncea with a mean of 0.47 parasitized larvae.