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%).