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.
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