ABSTRACT

Understanding the mechanism for resistance of weeds to herbicides is important in designing strategies to prevent the occurrence of herbicide-resistant weeds and to control them when they occur. Weeds have three physiological mechanisms for becoming resistant to herbicides, These include: 1) resistance at the molecular site of action, 2) enhanced metabolic degradation of the herbicide, and 3) limited movement of the herbicide to the site of action. Herbicide-resistant weeds may have any combination of these general mechanisms. If resistant weeds are resistant at the site of action, they are usually cross-resistant to all or most herbicides with the same mechanism of action. Multiple resistance to several herbicide classes can result from metabolic degradation mechanisms or combinations of several mechanisms of resistance.