Herbicide resistance is a worldwide phenomenon of great concern to scientists, technicians and producers. It is characterized as the capacity of a biotype to survive a treatment using herbicide that controls the other individuals of the same population under normal field conditions and at the dose recommended by the manufacturer. The objective of this research was to determine the resistance level of two Cyperus difformis biotypes to ALS-inhibiting herbicides. The herbicide treatments consisted of the application of bispyribac-sodium, pyrazosulfuron-ethyl, (ALS-inhibitors) and bentazon (photosystem II inhibitor) sprayed at seven multiple commercial doses (0,0x; 0.5x; 1x; 2x; 4x; 8x and 16x), on two plant populations of C. difformis, at the stage of four to six leaves. The CYPDI-10 biotype showed a crossed-resistance to the ALS- inhibiting herbicides pyrazosulfuron-ethyl and bispyribac-sodium, while bentazon showed an efficient control of the resistant and susceptible populations. It was concluded that for the correct management of ALS-resistant C. difformis biotypes in flooded rice areas of Santa Catarina, Brazil, the use of herbicides with different action mechanisms should be adopted, as well as other management practices in order to restrict the expansion of resistant populations of C. difformis.
crossed resistance; pyrazosulfuron-ethyl; bispyribac-sodium; smallflower umbrella sedge
