Resistance of weeds to ALS-inhibiting herbicides: what have we learned?

Herbicides that target the enzyme acetolactate synthase (ALS) are among the most widely used in the world. Unfortunately, these herbicides are also notorious for their ability to select resistant (R) weed populations. Now, there are more weed species that are resistant to ALS-inhibiting herbicides than to any other herbicide group. In most cases, resistance to ALS-inhibiting herbicides is caused by an altered ALS enzyme. The frequent occurrence of weed populations resistant to ALS inhibitors can be attributed to the widespread usage of these herbicides, how they have been used, the strong selection pressure they exert, and the resistance mechanism. In several cropping systems, ALS-inhibiting herbicides were…