Amaranthus hybridus MANAGEMENT IN CROP-LIVESTOCK SYSTEMS IN SOUTHERN RIO GRANDE DO SUL

Abstract

Recently, soybean cultivated area has risen in Brazil and so had total production. In the Rio Grande do Sul state (RS), soybean production is also increasing and its grown after beef production during the cold season, a production model that contributes to improve land usage during the twelve months of the year, increasing farmers’ income and, when well handled, it can also contribute to integrated weed management. Despite that, the presence of hard-to-control broadleaved weeds like Amaranthus hybridus in RS soybean fields its on the rise. Therefore, this study objective was to evaluate the efficiency of pre- and post-emergency herbicides, and different management programs on Amaranthus hybridus populations. The study was composed by four experiments, two under controlled conditions in a greenhouse and two on a farm in Cerrito, RS, that integrates soybean production with cattle livestock. The experiments show that some biotypes are tolerant to glyphosate and ALS inhibitors (imazethapyr and chlorimuron-ethyl), and that the use of the pre-emergence herbicides imazethapyr + flumioxazin, metribuzin, s-metolachlor e sulfentrazone + diuron contributes to the biotypes management. It was also verified that the ryegrass burndown and its complementation with contact and pre-emergence herbicides are determinant factors to control A. hybridus. Yet, the results point that under water deficit situations, straw presence can reduce the efficiency of some pre-emergence herbicides.