RESUMO
Cyperus difformis L. é planta daninha ocorrente em lavouras de arroz irrigado, que tem apresentado dificuldade de controle devido à resistência a herbicidas inibidores de ALS. O objetivo da pesquisa foi estimar a dose necessária para controlar 50% da população (C50) e reduzir 50% da produção de massa da parte aérea seca (GR50) em biótipo resistente e suscetível de C. difformis e avaliar o controle destes biótipos com herbicidas alternativos recomendados para a espécie. Para isso, foram conduzidos dois experimentos em casa de vegetação, em delineamento experimental completamente casualizado, com quatro repetições. O experimento I constou de biótipo resistente (CYPDI 9) e suscetível (CYPDI 8) de C. difformis e doses do herbicida pyrazosulfuron-ethyl, correspondendo a 0; 0,5; 1; 1,5; 2; 2,5; 3; 4; 6; 8; 16; 32 e 64 vezes a dose registrada (20 g ha-1). As variáveis avaliadas foram controle visual e massa da parte aérea seca (MPAS) aos 28 dias após a aplicação dos tratamentos (DAT). No experimento II os tratamentos constaram dos biótipos (CYPDI 9 e CYPDI 8), nove herbicidas: azimsulfuron (6g ha-1); bentazon (900g ha-1); bispyribac-sodium (48g ha-1); carfentrazone-ethyl (40g ha-1); ethoxysulfuron (72g ha-1); glyphosate (900g ha-1); penoxsulam (36g ha-1); propanil (3600g ha-1) e pyrazosulfuron-ethyl (20g ha-1) e testemunha que não recebeu herbicida. As variáveis avaliadas foram: controle visual aos 14, 21 e 28 DAT, área foliar (AF) e MPAS aos 28 DAT. A resistência do biótipo de C. difformis ao pyrazosulfuron-ethyl é elevada e inviabiliza seu controle pelo herbicida e, os herbicidas carfentrazone-ethyl, bentazon e propanil, detentores de mecanismos de ação alternativos ao pyrazosulfuron-ethyl, controlam o biótipo resistente de C. difformis.
Cyperus difformis L. is a weed occurrence in flooded rice, that it has been presenting control difficulty due to ALS inhibiting herbicides resistance. The objectives of this work was to determine necessary rate 50% control of the population (C50) and reduce 50% of the production the aerial dry mass (GR50) in resistant and susceptible biotypes of C. difformis and evaluate the control of these biotypes with alternative herbicides recommended for that species. For that, two experiments were performed at green house of FAEM/UFPel arranged in a completely randomized design, with four replicates. The experiment I were consisted of resistant (CYPDI 9) and susceptible of C. difformis biotype and rate of the pyrazosulfuron-ethyl herbicide, corresponding to 0, 0,5, 1, 1,5, 2, 2,5, 3, 4, 6, 8, 16, 32 and 64 times de registered rate (20g ha-1). The evaluated variables were visual control and aerial dry mass (MPAS) to the 28 days after the application of the treatments (DAT). In the experiment II the treatments were consisted of the same biotype (CYPDI 9 and CYPDI 8), nine herbicides azimsulfuron (6g ha-1); bentazon (900g ha-1); bispyribac-sodium (48g ha-1); carfentrazone-ethyl (40g ha-1); ethoxysulfuron (72g ha-1); glyphosate (900g ha-1); penoxsulam (36g ha-1); propanil (3600g ha-1) and pyrazosulfuron-ethyl (20g ha-1) and checks that didn't applied herbicide. The evaluated variables were: visual control for the herbicides to the 14, 21 and 28 DAT, foliate area and MPAS to 28 DAT. Before the results, it can be concluded that the resistance of the C. difformis biotype to pyrazosulfuron-ethyl is elevated and it makes unfeasible her control for the herbicide and the herbicides carfentrazone-ethyl, bentazon e propanil holders of alternative action mechanisms to the pyrazosulfuron-ethyl, control the resistant biotype of C. difformis.