Resistance to glyphosate in Conyza bonariensis and Conyza canadensis biotypes in Rio Grande do Sul, Brazil

Dose-response experiments were conducted to evaluate the occurrence of resistance to glyphosate in Conyza canadensis and Conyza bonariensis biotypes originated from Rio Grande do Sul counties. For each species, one experiment was conducted with two biotypes, one susceptible and one suspected of resistance. Glyphosate rates of 0, 100, 200, 300, 400, 800 and 1200 9 ha(-1) were sprayed on the plants after reaching the 8-10 leaf growth stage. Sigmoidal curves were adjusted to each biotype tested. Resistance to glyphosate was confirmed for biotypes of both species with resistance factor of 2.3.