Herbicides inhibiting acetyl-coenzyme A carboxylase (ACCase) or acetolactate synthase (ALS) are key for grass weed control. Yet, numerous cases of resistance have evolved. Using the derived cleaved amplified polymorphic sequence method, we developed molecular assays to detect amino acid replacements at the seven ACCase codons (1781, 1999, 2027, 2041, 2078, 2088 and 2096) and at two ALS codons (197 and 574) known to play a role in herbicide resistance in grass weeds. For each codon, one assay detecting all known amino acid replacements endowing herbicide resistance was developed. The nine assays were successfully used to genotype ACCase and ALS in 39 grass species. Their flexible design enables easy detection of new mutations at the targeted codons. Because they can be implemented with basic molecular biology facilities and no previous knowledge of the ACCase or ALS sequence of the grass weed of interest, these assays are tools of choice to easily detect resistance caused by alteration(s) of ACCase or ALS in such species.