Sicklepod (Senna obtusifolia) Control in Soybean (Glycine max) with Imazaquin and Metribuzin Combinations

Abstract

Field studies were conducted in 1993 and 1994 to evaluate sicklepod control with combinations of imazaquin + metribuzin at lower than normal use rates. Soybean was seeded in late-May to early-June each year and imazaquin and metribuzin were applied PPI alone at 0.75 and 1x and 0.5, 0.75, and 1x their registered rates, respectively, and in factorial combinations of their 0.5 and 0.75x rates. The registered (1x) rates for imazaquin and metribuzin on this soil type are 0.14 and 0.43 kg/ha, respectively. Several standard sequential treatments and flumetsulam + trifluralin PPI at 0.06 + 0.70 and 0.07 + 0.95 kg/ha were included for comparison. Sicklepod control and soybean seed yield responses differed between 1993 and 1994. In 1993, the combinations of imazaquin + metribuzin averaged 90% control 6 wk after planting (WAP) and soybean seed yield increased 75% compared to the untreated check. Imazaquin + metribuzin at their respective 0.5x rate was as effective as any treatment evaluated. In 1994, sicklepod control was generally lower with all treatments. Soybean seed yield was reduced due to sicklepod interference with soil-applied treatments alone. However, imazaquin + metribuzin at their respective 0.75x rate provided sicklepod control levels and reductions in weed biomass similar to those observed with flumetsulam + trifluralin at 0.07 + 0.95 kg/ha and the sequential treatments, and increased soybean seed yield 19% compared to the untreated check.