The continuous and prolonged use of products with the same mechanism of action can provoke the manifestation of resistant biotypes. In horder to verify possible new cases, as well as alternatives for prevention and control, seeds of Bidens subalternans were collected at São Gabriel D' Oeste (MS) region at plants that survived continuous treatments which sistematically ALS inhibitors. Through an experiment performed in pots inside a greenhouse, a resistant biotype was compared to a susceptible one when submitted to herbicides with different mechanisms of action and applied at post emergence. These herbicides were applied at doses zero, one, two, four and eight times the recommended dosage. Twenty days after, the control and the green weight production were analysed aiming to get the dose-response curves as well as the resistance factor. The biotype from the area with repeated application of ALS inhibitors showed a high level of resistance to chlorimuron-ethyl and imazethapyr, demonstrating therefore to be a carrier of crossed resistance to the ALS inhibitors of the sulfonilurea and imidazolinona groups. However, this biotype was controlled by fomesafen, lactofen, bentazon, ammonium glufosinate and glyphosate.
crossed resistance; sulfunylurea; imidazolinone
