Determination of minimum doses of post-emergence metribuzin used to control weeds in potato fields

This study was conducted to determine the minimum doses of post-emergence metribuzin giving satisfactory control efficacy (>90%) on Amaranthus retroflexus L. and Sinapis arvensis L., the two troublesome weeds of spring and autumn potato fields, respectively. Minimum doses of metribuzin was tested at 2-5- and 6-9-true leaf stages. The recommended dose of metribuzin was labelled as 35-52.5 g a.i./da by the producer company.Experiments were conducted in plastic pots kept in controlled greenhouses. 100, 80, 60, 40 and 20 % of the registered dose of metribuzin were applied and some were left untreated for control. Plants length, number of leaves and herbicide symptoms were measured at 1st, 3rd, 5th, 7th, 14th, 21st and 28th days. At the 28th day plants were cut at soil surface and fresh and dry weights were determined. Dry weight data of the experiments were subjected to nonlinear regression analyses and the effective doses of metribuzin causing 90% reduction in dry weight (ED90) were estimated from the dose-response curve.Results indicated that 24.1 g a.i./da metribuzin gives 90% reduction in the dry weight of A. retroflexus when applied at 2-5-true leaf stage, and to get same reduction at the 6-9-true leaf stage 29.3 g a.i./da metribuzin is required. When the problem weed is changed to S. arvensis, 18.4 g a.i./da and 25.6 g a.i./da metribuzin is needed to get 90% control at 2-5- and 6-9-true leaf stages, respectively.