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Resumo - Abstract -Alternatives for volunteer corn RR® management need further knowledge in the product scope with residual effect, mainly for use in pre-emergence of the soybean RR ® . This paper evaluated the performance of residual herbicides to control this species, when applied in soybean using the method "plant-apply". The experiment was carried in the municipality of Santa Maria/RS, crop season 2015/16; evaluating herbicides applied in pre-emergence of soybean crop and corn RR ® . The experimental design was randomized blocks with eight treatments and four replications were evaluated inhibition of emergence of corn plants and injury on emerged plants. Sequential application responses were also addressed. Herbicides tested: flumioxazin, chlorimuron-ethyl, imazaquin, and sulfentrazone; as associations these herbicides with flumioxazin, in sequential applications, reporting if there were synergistic effects. The best control of RR ® volunteer corn was obtained with the imazaquin herbicide, which reduced the emergence of RR ® corn plants by 90% and injured 97.5% of those that emerged. However, imazaquin caused symptoms of 1 Recebido para publicação em

Identification of Echinochloa spp. populations resistant and susceptible to acetolactate synthase-inhibiting and auxin-mimic herbicides Identificação de populações de Echinochloa spp. resistentes e suscetíveis a herbicidas inibidores da enzima acetolactato sintase e mimetizadores de auxina

This work aimed at determining possible resistance of three biotypes of Cyperus iria to inhibiting herbicides of acetolactate synthase enzyme (ALS). An experiment at greenhouse was conducted out where suspected resistance biotypes were multiplied through seeds in pots filled with soil. The treatments were arranged in a trifactorial (AxBxC) design, where factor A consisted of three biotypes of Cyperus iria, from three locations of the state of Rio Grande do Sul (named Santa Maria 1, São Borja 3 and Cachoeira do Sul 7). Factor B corresponds to three herbicides (pyrazosulfuron-ethyl, ethoxysulfuron and bentazon). Factor C refers to herbicide doses (zero, 50% of registered dose; registered dose, two, four and eight times registered dose of herbicides). For resistance measurement, it was used resistance factor calculation (RF) and for dose-response curves through regression analysis, RF on dry mass (DM) of plants. It was observed that São Borja 3 and Cachoeira do Sul 7 biotypes have a low resistance factor (1 < RF < 10) to pyrazosulfuron-ethyl and ethoxysulfuron herbicides. These showed lower susceptibility to ethoxysulfuron (RF = 5.49-6.76) than pyrazosulfuron-ethyl (RF = 2.21-2.47). The clear distinction in the susceptibility of biotypes, include responses of chemical control to field due to the long period of use of ethoxysulfuron herbicide. It is concluded that this factor characterizes low-level resistance, being a cross-resistance type, thus demonstrating the ineffectiveness of ALS-inhibiting herbicides to control this species.

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