The species of the genus Cyperus, Cyperaceae family, are the major weeds in the rice producing regions of the state of Rio Grande do Sul (RS). The objective of this study was to evaluate the diversity of Cyperus ferax in these regions and the sensitivity levels of this species to the herbicide penoxsulam. Thus, an experiment was conducted under greenhouse conditions in the Faculdade de Agronomia Eliseu Maciel. The experimental design was completely randomized, with four replications. Each experimental unit (plot) was composed of vases with a capacity of 0.55 dm³ of soil, with seven plants. Treatments were arranged in a factorial design.Factor A evaluated the places of collection (origin) of the seeds of C. ferax, a weed in RS irrigated rice fields; and factor B evaluated susceptibility to the herbicide penoxsulam (125 g ha-1), compared to a control without application. Differences were verified between the accessions of C. ferax regarding sensitivity to the herbicide penoxsulam. The biotypes from the irrigated rice fields at Depressão Central show, in general, higher shoot dry mass accumulation and leaf area. The C. ferax biotypes at the RS rice fields can be divided into two groups, according to their morphological characteristics.
chemical control; Cyperaceae; Oryza sativa; weed
