Field evaluation of an auto-rotate gun sprayer and comparison with a knapsack sprayer was carried out to control whitefly Bemisia tabaci (Genn.) in the cotton crop. Two experiments were conducted at six locations of farmers' fields in southwestern (cotton-growing region) of Punjab state. The number of adult whiteflies was counted before and 3, 7 and 10 days after spray. Water-sensitive papers were attached at upper and under side of the leaves at three different points (top, middle and bottom) of plant canopy to find sprayers performance parameters, viz. droplet diameter, droplet density, per cent area covered and volume of spray deposition. Droplet density, area covered and volume of spray deposition were found significantly higher in case of the auto-rotate gun sprayer as compared to that of a knapsack sprayer. However, the volume median diameter of droplets was found significantly lesser in case of an auto-rotate gun sprayer, i.e. 286.95 µm as compared to the knapsack sprayer, i.e. 347.85 µm. The per cent whitefly control in the cotton crop in first experiment was found as 68.06 % and 65.90 % for auto-rotate gun and knapsack sprayer, respectively, by using pyriproxyfen 100 g active ingredient (g a.i.)/ha. Although in the second experiment the per cent whitefly control for auto-rotate gun sprayer was significantly higher, i.e. 83.27 % as compared to knapsack sprayer having 70.87 % control by using flonicamid 75 g a.i./ha. However, the bio-efficacy of auto-rotate gun sprayer was found higher for the both experiments as compared to the knapsack sprayer. The cost of operation of the auto-rotate gun sprayer was found to be US$4.11/ha as compared to knapsack sprayer with $6.85/ha. The cost, labour and time-saving in the spraying with the auto-rotate gun sprayer as compared to the knapsack sprayer was found to be 39.98, 93.44 and 96.64 %, respectively.
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Vol. 28 • No. 2