PARAQUAT RESISTANCE IN A BIOTYPE OF VULPIA-BROMOIDES (L) GRAY,S.F.

A biotype of Vulpia bromoides from a lucerne field in Elmhurst, Victor ia, Australia was shown to be resistant to paraquat in pot trials. App lication of paraquat at 50 g a.i. ha-1 killed all of the plants of a s usceptible Vulpia bromoides biotype but only 6% of the resistant bioty pe. The LD50 for paraquat of the resistant biotype was five- to sixfol d higher than for the susceptible biotype. The resistant biotype was a lso resistant to the bipyridyl herbicide diquat, but was susceptible t o glyphosate and metribuzin. Application of 100 g a.i. ha-1 paraquat a t anthesis completely suppressed seed set of the susceptible biotype a nd reduced that of the resistant biotype by 95%. Seed set by the paraq uat-treated resistant biotype, however, showed little reduction in ger mination. This is the fourth species to have been found to be resistan t to bipyridyl herbicides in this field, the others being Hordeum glau cum, H. leporinum and Arctotheca calendula.