Sulfonylurea Herbicides' Fate in Soil: Dissipation, Mobility, and Other Processes

Sulfonylurea herbicides used in turfgrass—including chlorsulfuron, flazasulfuron, foramsulfuron, halosulfuron, metsulfuron, rimsulfuron, sulfometuron, sulfosulfuron, and trifloxysulfuron—are all weak acids, with disassociation constants ranging from 3.3 to 5.2. Sulfonylureas are used at low rates ranging from 4 to 280 g ha −1 . Although these use rates put their soil concentration in parts per billion, they still have residual activity with variable persistence. They have limited susceptibility to soil leaching with weak adsorption to soil clay minerals. Sulfonylurea herbicides used in turfgrass have variable soil organic matter adsorption, which is soil dependent. The persistence and activity of these sulfonylureas are affected by soil pH. At soil pH of 7.0 and greater, some of these sulfonylurea herbicides tend to persist for longer periods with half-lives extending into years rather than days. In normal use patterns with soil pH of 7.0 and less, dissipation occurs via chemical hydrolysis and microbial degradation with half-lives ranging from days to months. Overall, sulfonylurea herbicide adsorption is negatively correlated to increasing pH (increased persistence) and positively correlated to increased organic matter (decreased activity).