The monitoring of Echinochloa sp. plants resistant to quinclorac was conducted in Rio Grande do Sul and Santa Catarina, Brazil to determine the origin of resistance and its dissemination, as well as to detect practices or climatic conditions related to the selection and geographic distribution of the resistant biotype. The seeds were collected, purified and standardized, and trials conducted under growth chamber and greenhouse conditions. In the growth chamber, a standard germination test was conducted with the seeds being submitted to rates of 0x, 1x, 2x, 6x, 16x and 32x and to the recommended rate of quinclorac, followed by germination curve and seedlings survival evaluation 14 days after sowing (DAS); the same herbicide rates were evaluated under greenhouse conditions, applied over the plants 20 days after emergence (DAE). Dry weight and control were evaluated 35 DAE, and biotypes with RI above four were considered resistant. A map of both states was elaborated where distribution of resistance to quinclorac was showed graphically, followed by herbicide profoxydim test as an alternative for the resistant biotype control.
resistance index; flooded rice; control
