SURFACTANT STRUCTURE AND CONCENTRATION STRONGLY AFFECT RIMSULFURON ACTIVITY

A nonionic surfactant with the appropriate structure and concentration increased rimsulfuron activity 10-fold. Surfactants sharply increased rimsulfuron activity as concentration increased up to 0.05 % (w/w) wi th slightly more enhancement up to 0.1 % (w/w). Surfactants with a wid e range of 14 chemical, physical, and surface properties were evaluate d on giant foxtail, velvetleaf, and com. Two properties, HLB (hydrophi lic-lipophilic balance) and the physical form of the spray deposit, ex plained the biological variation. The most active surfactants had an H LB from 12 to 17 and formed a moist gel spray deposit on the leaf on a ll three species. A separate study with 13 chemically pure linear alco hol ethoxylates supported these conclusions and additionally showed th at increasing molecular size increases activity. Because crop injury c orrelates with weed control, the best surfactant strategy is to maximi ze weed control at the lowest rimsulfuron rate.