Primer reporte de resistencia de Cyperus odoratus L. al herbicida pirazosulfuron-etilo

First report of resistance of Cyperus odoratus L. to the herbicide pyrazosulfuron-ethyl The fragrant flatsedge (Cyperus odoratus L.) is one of the most common weeds in Venezuelan field rice, and we established two experiments in order to assess the weed resistance to the herbicide pyrazosulfuron-ethyl (sulfunylurea). The first was a dose response experiment using a susceptible (S) accession (CO338A) and a resistant one (R) (CO285P). In the second one, a third accession (CO286P)(R) was included, and the responses to alternative herbicides was explored. In the dose response experiment, the accession S was treated with 0; 0.390; 0.781; 1.562; 3.125; 6.25; 12.5; 25 g·ha -1 i.a. and the accession R with 0; 3.125; 6.25; 12.5 25; 50; 100; 200 g·ha -1 a.i. of pyrazosulfuron-ethyl, and 21 days after applications we determined aerial plant fresh weight expressed as percentage of the control treatment (no application). In the second experiment the accessions were treated with 25, 38.50+115.50, 40 and 540 g·ha -1 a.i. of pyrazosulfuron-ethyl, imazapyr+imazetapyr, carfentrazone-ethyl y 2,4 D-amine, and the percentage of control was measured. It was proved that the accession CO285P has evolved resistance to pyrazosulfuron-ethyl. Both R and S plants were controlled by imazapyr+imazetapyr, carfentrazona-ethyl and 2,4 D-Amine herbicides. The observed resistance responses reflects the intense use of ALS-inhibiting herbicides and indicates that programs combining cultural practices such as false planting and chemical control involving the use of herbicides with different mechanisms of action to inhibit ALS should be implemented to decrease the levels of resistance of C. odoratus in Venezuelan rice fields.