SOYBEAN (GLYCINE-MAX) CULTIVAR TOLERANCE TO SAN 582H AND METOLACHLOR AS INFLUENCED BY SOIL-MOISTURE

Field experiments were conducted in 1991 and 1992 to evaluate differential soybean cultivar tolerance to SAN 582H and metolachlor applied PRE, as influenced by soil moisture. Eighteen d after planting, a 3x rate of SAN 582H (3.0 kg ai ha(-1)) reduced plant populations of 'Wright,'Bedford, and 'Stonewall' and metolachlor did not. At leaf drop, neither herbicide reduced crop height with optimum moisture. With excessive moisture, 3x rates of SAN 582H reduced plant height of Wright, Bedford, (Walters,' 'Young,' 'Brim,' and 'Bryan,' and metolachlor reduced height of 'Sharkey.' The greatest yield reductions were due to excessive moisture, regardless of herbicide. Neither herbicide reduced yields with optimum moisture nor did a 1x rate with excessive moisture. However, with excessive moisture, a 3x rate of metolachlor (5.0 kg ai ha(-1)) reduced yield of Bedford by 470 kg ha(-1), and the 3x rate of SAN 582H reduced yield of 'Rhodes, 'Walters, and 'Centennial' more than 500 kg ha(-1). Overall, soybean tolerance to both herbicides was good, but if used above recommended rates and with excessive moisture, injury can occur.