Field studies were conducted in 1996 and 1997 at three locations throughout southern Ontario with the objective of developing dose-response curves of RPA 201772 for weed control and crop tolerance in corn. The biologically effective doses required to control redroot pigweed, velvetleaf, and wild mustard were 100, 90, and 80 g/ha, respectively. Yellow foxtail was controlled with 100 to 120 g/ha, while rates for common lambsquarters varied from 60 to 130 g/ha, depending on the year and location. Wild buckwheat control was poor (> 30%) at all of the doses tested. RPA 201772 did not reduce corn grain yield; however, temporary crop injury was evident on coarse sandy soils.

The relationship between surface activity and weed control efficacy of diuron spray solution (0.075 kg ai/ha) with 12 adjuvants (0.1% v/v) was studied in the laboratory and the greenhouse. Organosilicone adjuvants reduced surface tension (ST) and contact angle (CA) of diuron spray solutions to a greater extent than did nonsilicone adjuvants. Three organosilicone adjuvants significantly increased the control and reduced the fresh weight of barnyardgrass. Contact angle was more closely correlated with diuron efficacy than ST, and the coefficient of determination between the CA and the fresh weight or control percent of barnyardgrass was 0.41. Kinetic® applied before or in combination with diuron significantly enhanced diuron efficacy. However, Kinetic sprayed after diuron did not affect the efficacy. Kinetic influenced the retention and absorption of diuron rather than its deposition and translocation.