RESISTANCEOF BEGGARTICKS (Bidens subalternans L.) IN FARMING OF SOY OF RIO GRANDE DO SUL

Abstract

Weed herbicide resistance is a phenomenon defined as ability of a biotype survives to herbicide sprayed, at a recommended rate that control a susceptible population. This research had the objective of determine, the level of resistance the herbicides of the Bidens subalternans. The herbicides treatments they were with bentazon, fomesafen, imazethapyr e chloransulam-methyl. Sprayed in post-emergency, when B. subalternans reached stage four-leaf pairs. The herbicide rates sprayed was crescents in a logarithm scale of 0,0; 0,001; 0,01; 0,1; 1,0; 10 e 100 times of the control recommended rate. Through visual evolution and with aid of the percentile scale they were obtained the control data. The ratio between the C50 of the resistant biotype, and C50 of the susceptible biotype (R/S) were 0,79, 1,87, 53,69 and 486,02 to the herbicides bentazon, fomesafen, imazethapyr and chloransulam-methyl, respectively. The weed herbicide resistance happen in Rio Grande do Sul soybean fields and the biotypes R of B. subalternans presented high level of cross-resistance the herbicides inhibitions of ALS, of the chemical groups of the imidazolinones and sulfonanilides.