Full explanation
The HRAC (Herbicide Resistance Action Committee) system classifies herbicides into 34 groups by mode of action. For example, Group 1 is ACCase inhibitors (graminicides), Group 2 is ALS inhibitors (sulfonylureas), Group 9 is glyphosate, Group 10 is glufosinate. Repeated use of a herbicide from a single group drives weed resistance within 5–10 seasons. To prevent resistance, rotate products across different groups year-to-year and use the 'mixture' tactic — applying two active ingredients from different groups in the same pass. Documented Ukrainian resistance: ragweed to Group 2, pigweed to Group 2 + Group 9 (glyphosate+ALS).