Field persistence studies with emulsifiable concentrate and granular formulations of the herbicide pendimethalin in Saskatchewan

Studies were undertaken to evaluate the dissipation of pendimethalin (1.1 kg ha -1 ) in two Saskatchewan field soils following applications of an emulsifiable concentrate (EC) formulation in the spring. Persistence of pendimethalin applied as a granular formulation in the fall was also investigated at one of the locations. The EC formulation was applied in May, 1993, and by late September, 0.50 ± 0.16 kg ha -1 (41 ± 13% of that applied) remained at the Estlin site, and 0.34 ± 0.07 kg ha -1 (31 ± 6%) remained at the Regina location. Over the winter, there was little further loss of pendimethalin at either locality. By September, 1994 (479 days after treatment), 0.34 ± 0.07 kg ha -1 (28 ± 6% of the applied herbicide) remained at Estlin and 0.13 ± 0.05 kg ha -1 (12 ± 4%) remained at Regina. Some overwinter dissipation of pendimethalin occurred from a granular formulation (1.51 kg a.i. ha -1 ) applied at Regina on October 4, 1993, with 1.01 ± 0.15 kg ha -1 (67 ± 10% of the initial treatment) remaining in May, 1994. By the third week in September, 1994, 350 days after application, 0.45 ± 0.08 kg ha -1 (30 ± 5% of the initial herbicide) remained. Over the 479-day EC formulation and the 350-day granular formulation study periods, there was no leaching of the herbicide below 10 cm.