Also phytotoxicity from soil-applied herbicides that offer full season activity or from multiple applications made during the growing season can intensify the resistant weed biotype selection process. Although herbicides select for resistant biotypes, they probably do not directly cause the genetic mutation in the resistant biotypes. Resistance mechanisms differ with herbicide families. Resistant biotypes may possess small biochemical differences from susceptible counterparts that eliminate sensitivity to specific herbicides. Plants resistant to sulfonylurea herbicide have a modified ALS enzyme that prevents herbicide binding.
Enzymes function as steps in biological processes.
Enzymes are also extremely specialized in their function. As a result, different enzymes are involved with the many different biological processes that occur within a plant. This herbicide-enzyme relationship is very specific and any chemical modification of the herbicide or enzyme can eliminate herbicidal activity. Regardless of how resistance develops, it is important to know the herbicide mode of action to plan weed control programs that prevent the development and spread of resistant weeds. Weed control programs should incorporate a variety of strategies that emphasize prevention.