Interaction between saflufenacil and imazapyr+imazapic in the management of barnyardgrass and weedy rice and selectivity for irrigated rice/Interacao entre saflufenacil e imazapyr+imazapic no manejo de capim-arroz e arroz-daninho e a seletividade para cultura do arroz irrigado

The use of imidazolinone-tolerant rice cultivars allows selective control of weedy rice and barnyardgrass. However, in many situations, there is a need to add herbicides from other chemical groups to increase the spectrum of weed control. In this sense, saflufenacil has the potential to be used in mixture with imidazolinone herbicides. This study aimed to evaluate the interaction effects of the imazapyr+imazapic and saflufenacil herbicides in weedy rice and barnyardgrass and to investigate their impacts on the yield of the irrigated rice cultivar Puita INTA CL. To reach these aims, greenhouse and field experiments were carried out during two growing seasons, with herbicide treatments sprayed separately and in mixtures of saflufenacil with imazapyr+imazapic. Results showed that saflufenacil did not interfere with control of weedy rice and barnyardgrass obtained with imazapyr+imazapic. The [D.sub.50] values of imazapyr+imazapic for weedy rice control were 14.5+5, 9.1+3 and 12.5+4.2 g [ha.sup.-1] of imazapyr+imazapic for combinations with 0, 3.06 and 6.12 g [ha.sup.-1] of saflufenacil, respectively. In thefield experiments, all doses of imazapyr+imazapic applied isolated or in mixture with saflufenacil provided control levels barnyardgrass above 90% at 28 days after herbicides application. Furthermore, saflufenacil did not cause damage or loss in the yield of the rice crop when mixed with imazapyr+imazapic. The Puitd INTA CL rice cultivar was tolerant of the tested herbicides, whether applied alone or in mixture, reaching grain yield of 9.987 kg [ha.sup.-1] when applied 42 g [ha.sup.-1] of saflufenacil plus 147+49 g [ha.sup.-1] of imazapyr+imazapic. Key words: herbicides, imidazolinone, pyrimidinedione, Oryza sativa. A utilizagao de cultivares de arroz tolerantes as imidazolinonas possibilita um controle seletivo de arroz-daninho. No entanto, em muitas situacoes existe a necessidade de adigao de herbicidas de outros grupos quimicos para aumentar o espectro de controle de plantas daninhas. Neste sentido, saflufenacil apresenta potencial para ser utilizado em mistura com herbicidas imidazolinonas. Este estudo teve como objetivo avaliar os efeitos da interacao dos herbicidas imazapyr+imazapic e saflufenacil em arroz-daninho e capim-arroz; e averiguar os impactos sobre a produtividade do cultivar de arroz irrigado Puitd INTA CL. Para alcangar esses objetivos, foram realizados experimentos em casa de vegetagao e a campo em duas estacoes de cultivo, com os tratamen