Control of wheat midge, Sitodiplosis mosellana (Gehin), at lower chemical rates with small-capacity sprayer nozzles

A three-year study was conducted to identify methods of applying sprays at lower chemical rates for control of wheat midge, Sitodiplosis mosellana (Gehin). Tracer dye experiments focused on methods of increasing the volume and reducing the variation of deposits on wheat heads, the primary target of field sprays against wheat midge. Deposits increased from 2.6 mu l to 4.6 mu l when 8002F nozzles, spaced 0.51 m apart, were directed 40 degrees forward rather than 10 degrees forward. Deposits declined from 5.4 mu l with a 0.35 m spray path, the forward diagonal distance between nozzles and base of wheat heads, to 4.4 mu l with a 0.45 m or 0.60 m path. A 0.45 m path reduced the variation to 9.7%. Deposits from 8001F nozzles, spaced 0.255 m apart, increased from 2.9 mu l to 5.2 mu l when nozzles were reoriented from 10 to 40 degrees forward. Deposits increased curvilinearly from 4.7 mu l with a 0.15 m path to 6.1 mu l and 5.1 mu with 0.30 m and 0.35 m, paths, respectively. A 0.35 m path reduced variation to 9.2%. Different settings were required for uniform deposits on horizontal and vertical paper targets. In four field tests, recommended and reduced rates of chlorpyrifos were applied with a track sprayer or field sprayer fitted with 8001F nozzles spaced 0.255 m apart. Nozzles were directed 40 degrees forward, 0.20-0.25 m above the crop to provide a 0.32-0.37 m spray path. Assessments of midge larvae and damaged kernels indicated that the rate of chlorpyrifos can be lowered from 0.40 to 0.24 kg Al ha(-1) with little or no loss in control and protection. Differences in midge damage between the two rates never exceeded 2%. Therefore, nozzle settings that increased deposits on the biological target also facilitated lower chemical rates without compromising efficacy. Lower chemical rates would reduce control costs and environmental contamination and may improve the compatibility of chemical and biological controls. Crown copyright (C) 1997 Published by Elsevier Science Ltd.