Alternative control of two biotypes of Echinochloa phyllopogon susceptible and resistant to fenoxaprop-ethyl.

Rice (Oryza sativa var.), is one of the most important crops worldwide, and is cultivated in the five continents since it adapts itself to all climatic conditions. The most important weeds that reduce the world rice yield are Echinochloa spp., annual gramineae, which, because of the selection pressure imposed on them, have developed resistance to a large series of herbicides. Two Echinochloa phyllopogon biotypes were studied, one of them resistant to molinate, thiobencarb and fenoxaprop-ethyl and the other one susceptible to these herbicides, both originating from California rice fields. In these biotypes, the effects of other herbicides were evaluated, some of them with the same mode of action [profoxydim (Aura) and cyhalofopbutyl (Clincher), both ACCase inhibitors] and others with different modes of action [quinclorac (Facet) belonging to auxinic herbicide families; bispyribac-Na (Nominee) and azimsulfuron (Gulliver), both ALS inhibitors]. The only herbicide that effectively controlled the R biotype was profoxydim (95% control). Cyhalofop-butyl, quinclorac and bispyribac-Na did not control the R biotype by more than 40%. There is no doubt that azimsulfuron hardly had any effect (14%). On the other hand, in the S biotype, three herbicides were quite effective: profoxydim (93%), quinclorac (93%), and cyhalofop-butyl (90%). Bispyribac-Na and azimsulfuron hardly had any effect on the S biotype, with no significant differences in either herbicide (20%).