Diclofop‐methyl resistance in populations of Lolium spp. from central Italy

Populations of Lolium spp. collected in central Italy were screened for resistance to acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides and compared with known susceptible and resistant Lolium rigidum (Gaud.) populations from Australia. Populations Roma’94 and Tuscania’97 were up to 8‐ and 7.5‐fold more resistant to diclofop‐methyl, respectively, than susceptible populations in pot experiments. However, populations Tarquinia’97 and Vetralla’94 were not resistant. Diclofop‐methyl resistance levels in the Italian populations were lower than in the Australian populations SLR31 and WLR96 (16.5 and > 64 times more resistant than S respectively). In an agar germination test, Tuscania’97 showed low levels of cross‐resistance to fluazifop‐p‐butyl, whereas no cross‐resistance was found in the Roma’94 population.