Effect of swath width, time of application and height on the efficacy of very-low-volume (VLV) water-based insecticides on cotton in Malawi

Abstract

The effects of the variation of swath width, time during the day when sprays were applied and nozzle height above the crop canopy were investigated when applying very-low-volume (VLV; 3–121 ha −1) water-based insecticide sprays to cotton using hand-carried spinning-disc sprayers at Chitala, Kasinthula and Makoka Research Stations, Malawi in 1976/77 and 1977/78. At Chitala, control of Aphis gossypii Glover and major bollworms, Diparopsis castanea Hampson and Heliothis ( Helicoverpa) armigera Hübner, was better when holding the nozzle at 1 m than at 0.5 m above the crop canopy but yield of seed cotton was significantly higher at 0.5 m in one season only. Control of major bollworms was not affected by changes in swath width or time of day when spraying occurred but at Makoka the two-row swath width gave the best Earias spp. control in one season only. The lowest yield of seed cotton was when spraying a four-row swath width early in the season at Makoka in 1976/77 only. Bemisia spp. control was better at Makoka when spraying before 0830 h whereas Earias control was poorest in 1976/77 when spraying between 1600 and 1800 h at Kasinthula. At Chitala, Aphis control was poorest when spraying before 0830 h. Significant interactions were few and inconsistent.