SULFONYLUREA HERBICIDES SUPPRESS DOWNY BROME (BROMUS-TECTORUM) IN WINTER-WHEAT (TRITICUM-AESTIVUM)

In separate studies in west-central Kansas, a prepackaged mixture of c hlorsulfuron + metsulfuron (5:1 w/w) and triasulfuron alone or in comb ination with metribuzin as a sequential or tank mix treatment were eva luated two years for downy brome control in winter wheat. Downy brome and wheat responses to each herbicide alone PRE or plus metribuzin POS T varied between years. Visually, downy brome biomass was reduced 32 t o 79% by chlorsulfuron + metsulfuron at 16 to 26 g ai/ha and 58 to 76% by triasulfuron at 30 g ai/ha applied PRE. Metribuzin POST at 158 g a i/ha following chlorsulfuron + metsulfuron PRE at 26 g/ha and metribuz in POST at 140 g/ha or more following triasulfuron PRE at 30 g/ha redu ced downy brome biomass in both years more than PRE treatments alone. Chlorsulfuron + metsulfuron at 11 or 16 g/ha plus metribuzin at 105 or 158 g/ha applied POST affected downy brome less in 1992 than chlorsul furon + metsulfuron applied PRE at 21 or 26 g/ha. Conversely in 1993, POST treatments except for chlorsulfuron + metsulfuron at 11 or 16 g/h a plus metribuzin at 105 g/ha affected downy brome more than PRE treat ments. Triasulfuron plus metribuzin POST in late fall controlled downy brome better than a sequential application in one of two years; late- fall POST was better than early-spring POST applications in both years . Despite some treatments retarding growth, no treatment in either stu dy reduced wheat yield in 1992. However in 1993, chlorsulfuron + metsu lfuron PRE at 26 g/ha, chlorsulfuron + metsulfuron at 16 g/ha plus met ribuzin at 105 or 158 g/ha applied POST, and metribuzin POST at 315 g/ ha reduced wheat yields. Triasulfuron at 30 g/ha plus metribuzin at 14 0 g/ha or higher applied PRE, sequentially, or POST in late fall and m etribuzin applied POST in early spring at 280 g/ha also reduced wheat yields.