SOYBEAN (GLYCINE-MAX) RESPONSE TO THIFENSULFURON AND BENTAZON COMBINATIONS

Field studies were conducted in 1995 and 1996 at three locations in Il linois to determine soybean response to combinations of thifensulfuron and bentazon. Thifensulfuron was applied at 2.2 to 8.8 g ai/ha alone or in combination with 280 to 560 g/ha of bentazon. Soybean injury 30 d after treatment ranged from 0 to 22% when thifensulfuron was applied alone at 2.2 g/ha. increasing thifensulfuron rate to 8.8 g/ha increas ed soybean injury to a range of 12 to 44%. Soybean grain yield was sig nificantly reduced compared to the yield of untreated soybean when thi fensulfuron was applied at 4.4 and 8.8 g/ha in two of five and four of five experiments, respectively. The addition of bentazon to thifensul furon consistently reduced soybean injury and stunting. In many cases, increasing the bentazon rate to 420 g/ha decreased soybean injury fro m thifensulfuron to a greater extent than 280 g/ha. In cases where thi fensulfuron decreased soybean yield, the addition of 420 or 560 g/ha o f bentazon restored yields to levels that were not lower than untreate d soybeans. These studies demonstrate that thifensulfuron at 2.2 to 8. 8 g/ha in combination with bentazon at 420 g/ha may be safely applied to soybean for broadleaf weed control.