Dose-response curves of a resistant Brachiaria plantaginea biotype to ACCase inhibitor herbicides

Abstract

 The development of a Brachiaria plantaginea resistant biotype to ACCase inhibitor herbicides has occurred in several soyabean production areas in Brazil, especially in Paraná State. However, little research has been conducted in order to prove scientifically the resistance using dose-response curves. In order to draw dose-response curves and determine GRso and GRso of a suspected 8. plantaginea biotype, herbicides of the chemical groups ariloxyphenoxypropionic acid (haloxyfop-rnethyl, quizalofop-p-ethyl, fluazifop-p-butil and fenoxaprop-p-ethyl) and cyclohexanodiones (sethoxydim, clethodim and butroxydim) were sprayed at rates of 0.1, 1.0, 10 and 100 times the recommended rate. The experiment was installed in the greenhouse of the Plant Production Department of USPIESALQ, in 500 ml plastic pots. The herbicides were sprayed at postemergence when the weed was at 2 to 3 shoot stage. The Brachiaria plantaginea biotype studied showed cross resistance to both ACCase inhibitor herbicides; however, the degree of resistance varied among the individual herbicides.