Efficacy and sugarbeet tolerance with postemergence dimethenamid-P

Field experiments were conducted from 1998 to 2000 to evaluate crop tolerance and weed control from dimethenamid-P alone and in tank-mix combinations applied postemergence (POST) to sugarbeet (Beta vulgaris L.) at Ontario, Oregon. In the tolerance trials dimethenamid-P was applied to four- to six-leaf sugarbeet in 1998 and 1999 and to two- to four-leaf sugarbeet in 2000. Significant (P < 0.05) herbicide injury to sugarbeet was observed in 1998 and 2000 at both 12 and 28 days after treatment (DAT). Sugarbeet injury was not significant for any herbicide treatment in 1999. Dimethenamid-P applied at 2.87 kg ha -1 caused the greatest sugarbeet injury in 1998. Injury in 2000 from tank-mix combinations of dimethenamid-P at 0.72 kg ha -1 plus desmedipham-phenmedipham with and without triflusulfuron was greater than from dimethenamid-P at 2.87 kg ha -1 at 12 DAT and similar at 28 DAT. Sugarbeet yield from plots treated with dimethenamid-P at 2.87 kg ha -1 was less than all other treatments in 1998. In 1999, plots treated with dimethenamid-P at 1.43 kg ha -1 produced greater root and estimated recoverable sucrose yields than untreated plots or those treated with dimethenamid-P at 0.72 kg ha -1 . Sugarbeet yields did not differ among treatments in 2000. In the weed control trials dimethenamid-P at 0.72 kg ha -1 was applied to two- to four- or four- to six-leaf sugarbeet. Dimethenamid-P added to desmedipham-phenmedipham increased late season barnyardgrass control by 34 and 32% in 1998 and 1999, respectively. Late season barnyardgrass control increased 22% in 1998 and 85% in 1999 when dimethenamid-P was added to desmedipham-phenmedipham plus triflusulfuron. Sugarbeet root yields in plots treated with POST combinations plus dimethenamid-P ranged from 7.4 to 9.6 Mg ha -1 higher than those same POST combinations without dimethenamid-P in 1998 and 1999. Sugarbeet root yields were greater (P < 0.1) when dimethenamid-P was applied with desmedipham-phenmedipham in 1998 and 1999 and with desmedipham-phenmedipham plus triflusulfuron in 1999. Desmedipham-phenmedipham plus triflusulfuron plus dimethenamid-P applied to two- to four-leaf sugarbeet provided significantly (P < 0.15) greater root yield than the same treatment without dimethenamid-P in 1998. The trend toward higher root yields was likely due to greater redroot pigweed, hairy nightshade, and barnyardgrass control in 1998 and greater barnyardgrass control in 1999 from dimethenamid-P.