Nicosulfuron and primisulfuron are sulfonylurea herbicides that may persist in the soil and injure sensitive rotational crops such as sugarbeet. Studies were initiated to measure sugarbeet response one and two years after application of 70 and 140 g/ha of nicosulfuron and 40 and 80 g/ha of primisulfuron to corn. Nicosulfuron did not injure sugarbeet one or two years after application. In contrast, sugarbeet yield was reduced one year after application of 40 and 80 g/ha of primisulfuron. Injury was visible two years after application of 80 g/ha primisulfuron but this did not cause a yield reduction. In greenhouse studies, the concentration of nicosulfuron and primisulfuron that reduced sugarbeet growth by 50% were determined for six soils. Primisulfuron reduced sugarbeet growth more than nicosulfuron on four of six soils indicating greater potential for sugarbeet injury from primisulfuron. Sugarbeet response was highly correlated with soil organic matter content (R2= 0.88). The sorption coefficients, Kdvalues, for nicosulfuron were 0.30 to 2.58 and the Kdvalues for primisulfuron were 0.76 to 3.47. Primisulfuron Kdvalues were higher than those of nicosulfuron on four of five soils indicating stronger affinity of primisulfuron for soil sorptive sites. The Kdvalues for both herbicides indicate low overall sorption. The greater sugarbeet injury observed in the field from primisulfuron is not due to greater availability of primisulfuron compared to nicosulfuron.

In preliminary field trials, a reduction in grass control was observed when flumetsulam or MON 12037 with and without the safener MON 13900 was applied with metolachlor compared to metolachlor alone. Greenhouse studies were initiated to study potential interactions between acetolactate synthase (ALS)-inhibiting herbicides and metolachlor. Metolachlor at 0.14, 0.28, and 0.56 kg ai/ha was applied alone and in combination with flumetsulam at 0.0073 and 0.015 kg ai/ha and MON 12037 with safener at 0.011 and 0.021 kg ai/ha. Flumetsulam and MON 12037 with safener alone provided 13 to 23% visible barnyardgrass control and metolachlor at 0.14 kg/ha provided 82% control. Combining flumetsulam and MON 12037 with metolachlor did not increase herbicide activity beyond that observed from metolachlor alone, regardless of the parameter evaluated. Combinations of 0.14 kg/ha of metolachlor with 0.011 and 0.021 kg/ha of MON 12037 with safener or 0.015 kg/ha of flumetsulam resulted in antagonism of barnyardgrass according to Colby's multiplicative interactive model. Visible control and plant dry weight were also antagonized when 0.28 kg/ha of metolachlor was applied with 0.021 kg/ha of MON 12037 with safener. Field studies were conducted in corn and soybean to evaluate giant foxtail control from metolachlor alone and in tank mixtures with flumetsulam, chlorimuron and MON 12037 with and without safener. Although isolated incidences of antagonism were noted, there was no consistent effect on grass control when these ALS-inhibiting herbicides were applied in combination with metolachlor in 3 years of field trials.

Field studies have shown primisulfuron to be more injurious to sugarbeet than nicosulfuron 1 and 2 yr after herbicide application. Experiments were initiated to determine if primisulfuron is more injurious to sugarbeet grown in a nutrient culture and if the difference in sugarbeet response is a result of greater uptake, translocation, or acetolactate synthase (ALS) site sensitivity with primisulfuron. Concentrations of primisulfuron and nicosulfuron that reduced sugarbeet growth by 50% were 1.9 and 8.9 μg ai L−1, respectively, at pH 6.5. The pH of the nutrient solution did not influence sugarbeet response to either herbicide. Uptake of primisulfuron was greater (3%) than that of nicosulfuron (1%). Translocation (expressed as a percent of uptake) of nicosulfuron was more rapid than primisulfuron. Fifty-seven percent of the absorbed nicosulfuron translocated out of the root during the 12-h pulse period, while an equal concentration of primisulfuron was not translocated out of the root until 48 h after pulsing. The total nicosulfuron translocated after 144 h was half that of primisulfuron. The nutrient solution taken up by sugarbeet in the 12-h pulse period was reduced by 41% in the presence of either herbicide compared to the untreated control. The ALS enzyme was a minimum of 15 times more sensitive to primisulfuron compared to nicosulfuron which may account for greater sugarbeet response to primisulfuron.