Identification of Echinochloa spp. populations resistant and susceptible to acetolactate synthase-inhibiting and auxin-mimic herbicides

This study evaluated the control of Echinochloa spp. collected in four irrigated rice producing regions of Rio Grande do Sul State, Brazil. We identified populations susceptible and resistant to the herbicides quinclorac (auxin mimic), bispyribac-sodium, penoxsulam, and imazethapyr (ALS inhibitors). The experiment was car­ried out in a greenhouse in a randomized block design with four replicates. Treatments were arranged in a 40x4x6 factorial scheme (40 populations, 4 herbicides, and 6 rates, corresponding to zero, one-half label rate, full label rate, and two, four, and eight times the label rate of each herbicide tested). Echinochloa spp. plants were counted and collected 25 days after emergence. Percent damage was analyzed as a function of plant dry mass. The dose-response curves showed different resistances between the populations collected in the different regions. The Central Depression region accounted for a higher number of populations re­sistant to ALS-inhibiting herbicides. Some Echinochloa spp. populations showed multiple resistance to ALS inhibitors and auxin mimics. Thus, the identification of resistant and susceptible populations and their regions of occurrence allows for more environmentally appropriate weed management.