MON-37500 RATE AND TIMING AFFECTS DOWNY BROME (BROMUS-TECTORUM) CONTROL IN WINTER-WHEAT (TRITICUM-AESTIVUM)

Field experiments were conducted at five locations in Colorado, Kansas , and Wyoming in 1994-1995 and 1995-1996 to compare the effects of MON 37500 rate and application timings on downy brome control and winter wheat tolerance. MON 37500 at 18 to 35 g ha(-1) applied preemergence o r fall postemergence reduced downy brome density 71 to 92% in 1995. Sp ring-applied MON 37500 suppressed downy brome growth but did not reduc e plant density. No application reduced downy brome density in 1996. A t each location, downy brome was controlled best by MON 37500 applied preemergence or fall postemergence at 35 g ha(-1). MON 37500 did not a ffect wheat height at Archer or Torrington, WY, and Burlington or Stra tton, CO, but wheat treated preemergence or fall postemergence wry; ta ller than untreated wheat at Hays, KS, in 1995. Spring-postemergence-c reated wheat at Hays in 1995 was shorter than untreated, preemergence- , or fall-postemergence-treated wheat. Wheat head density did not diff er among treated and untreated plots at Torrington, but herbicide trea tment increased wheat yields. Wheat head density increased with all MO N 37500 treatments at Hays in 1995, as did yield. However, preemergenc e and fall-postemergence applications resulted in the highest wheat yi elds. No herbicide treatment affected head density or yield at Hays in 1996.