Capim-amargoso no Rio Grande do Sul: resistência, crescimento e controle

Abstract

Weeds compete with the crop for light, water and nutrients, so they have a negative impact on crop yield. With the advent of transgenic crops, herbicides have become the main tool for weed control. However, the indiscriminate use of the same mechanism of action, combined with the incorrect use of technologies, accelerated the appearance of several resistant weeds, which created a serious problem in areas of agricultural production. Among the resistant weeds, there is the sourgrass (Digitaria insularis (L.) Fedde), a perennial plant that is difficult to control and quickly disseminated. This study was developed with the objectives of verifying the presence of glyphosate-resistant biotypes in Rio Grande do Sul; determine whether there are differences in the development of D. insularis biotypes from Mato Grosso (MT), Paraná (PR) and Rio Grande do Sul (RS); and seek alternatives for pre- and post-emergence control for this weed. The experiments were carried out in a greenhouse at the FAMV-UPF Extension and Agricultural Research Center (CEPAGRO) and in the field in Paraíso do Sul (RS). In the dose-response curve experiment, 10 treatments were used, being 0; 480; 960; 1,920; 3,840; 7,680; 15,360; 30,720; 61,440; 122,880 g ae/ha of glyphosate, in a completely randomized design with 4 replications. Through the results, it is observed that the biotypes R1, R2, R3, R4, and R5 are resistant to glyphosate, presenting a high resistance factor and LD50. In the growth analysis of the MT, PR and RS biotypes it was possible to observe that the sourgrass shows a greater increase in dry matter of shoots and roots in the summer/autumn period. However, in the spring/summer period, the development stages have an early start. In addition, the RS biotype presents more vigorous plants in the summer/autumn compared to the other tested biotypes. While the biotype of Mato Grosso shows similar development in summer/autumn and spring/summer, being more adapted to climate change. From the study of control alternatives for D. insularis, it is possible to infer that the herbicides S-metolachloro, imazapic + imazapyr, clomazone and imazethapyr + flumioxazin can be used for the efficient control of this invader in pre-emergence, without causing damage to the culture of soy. For the post-emergence application, the herbicides clethodim and haloxifop-methyl present efficiency of control in the stage of 3 to 4 leaves, being this the best period for the control of sourgrass. However, in perennialized plants it is necessary to carry out sequential applications and mixtures of herbicides, and the isolated application of the tested assets is not feasible.