Abstract: Greenhouse experiments were conducted in Greece to evaluate the level of propanil resistance in three barnyardgrass biotypes collected from rice fields where propanil had been used for around 25 yr. Suspected resistant biotypes were not controlled by propanil at 2.6, 5.2, 10.4, and 20.8 kg ai/ha, with the highest rate five times greater than the recommended rate. Control was reduced even more when propanil application was delayed until the three- to five-leaf stage. The susceptible barnyardgrass biotype collected from a nontreated propanil area was controlled with 2.6 kg/ha propanil. All barnyardgrass biotypes were effectively controlled by quinclorac (0.75 kg ai/ha) applied either alone at the two- to three-leaf stage or in mixture with propanil (3.5 kg/ha) at the three- to five-leaf stage. Only two of the resistant barnyardgrass biotypes were effectively controlled by azimsulfuron (0.02 kg ai/ha) applied alone at the two- to three-leaf stage, but all biotypes were controlled with the addition of propanil (3.5 kg/ha) at the three- to five-leaf stage. The resistant barnyardgrass biotype, which required the highest rate of propanil to reduce biomass by 50%, also tended to exhibit the most growth potential 7 to 22 d after emergence when compared with the other resistant biotypes or the susceptible biotype. Results clearly show that varying levels of barnyardgrass resistance to propanil exist but that effective control alternatives are available.
Nomenclature: Azimsulfuron; propanil; quinclorac; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; rice, Oryza sativa L.
Additional index words: Herbicide resistance, resistant biotype.
Abbreviations: DAE, days after emergence; R-BYG, resistant barnyardgrass; S-BYG, susceptible barnyardgrass.