Variation in ethofumesate tolerance in Lolium species and cultivars

The ethofumesate tolerances of seventy cultivars of Lolium perenne L., L. multiflorum Lam. and L. x hybridum Hausskn. were investigated by growing seedlings in a glasshouse in a potting compost treated with a critical level of the herbicide. The incidence of seedling deformity and death varied among cultivars, and was generally higher in diploids than in tetraploids, and in L. perenne than in L. multiflorum. Cv. Palaver was outstandingly tolerant. Eight cultivars were re-tested in pre- and post-emergence field experiments and relative tolerances were similar to those observed in the glasshouse. At the recommended doses for selective weed control, ethofumesate caused some seedling death in susceptible varieties in the pre-emergence experiment, and both seedling death and reduced herbage production in the post-emergence experiment. It is concluded that both varietal genotype and environmental factors contribute to the risk of ethofumesate damage in the field.