Field trials were conducted at five sites from 2001 through 2003 to determine the influence on sugarbeet and weeds of repeated broadcast and banded reduced rates of desmedipham plus phenmedipham, triflusulfuron, and clopyralid in combination with either 1.5 or 3% v/v methylated seed oil (MSO). Desmedipham plus phenmedipham, triflusulfuron, and clopyralid were applied POST three times at 5 to 7 d intervals at either 25, 50, 75, or 100% of a 180 plus 180 plus 18 plus 100 g ai/ha dosage (full rate). When averaged over all herbicide rates, crop injury was 6% greater, but common lambsquarters control was 5% higher, and crop yield was 15% greater with broadcast compared with banded herbicide application. In most situations, adding MSO at 3% rather than 1.5% did not improve weed control. Sugarbeet injury was lowest (11%) and the average weed control was 86% when herbicide rates (with 1.5% MSO) were 25% of the full rate (microrate). Applying an herbicide rate (with 1.5% MSO) that was 50% of the full rate (half rate) increased crop injury from 11% with the microrate to 18% with the half rate and elevated average weed control from 86% with the microrate to 92% with the half rate. Common lambsquarters control increased from 81% with the microrate to 89% with the half rate. Sugarbeet root yield was 23 t/ha when no herbicide was used, 48 t/ha with the microrate, and 49 t/ha with the half rate compared with 54 t/ha when the full rate was applied without MSO. Increasing herbicide rates to 75% of the full rate (three-quarter rate) (with 1.5% MSO) increased crop injury to 27% and average weed control to 96%. Applying 1.5% MSO to the full rate increased crop injury to 35% with no improvement in average weed control over that achieved with the full rate without MSO.
Nomenclature: Clopyralid; desmedipham; phenmedipham; triflusulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; sugarbeet, Beta vulgaris L. ‘Beta 1775’, ‘Beta 4546’, ‘HM1639RZ’.
Additional index words: Adjuvants, crop tolerance, crop yield.
Abbreviations: DAT, days after treatment; full rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 180 plus 180 plus 18 plus 100 g/ha; half rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 90 plus 90 plus 9 plus 50 g/ha; microrate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 45 plus 45 plus 4.5 plus 25 g/ha; MSO, methylated seed oil; three-quarters rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 135 plus 135 plus 13.5 plus 75 g/ha.