Diagnóstico do manejo e ocorrência de plantas daninhas em arroz irrigado no sul do Brasil

Abstract

The monoculture of the Clearfield® rice system, associated with the exclusive use of herbicides from the chemical group of imidazolinones, for the management of weeds, is not a sustainable strategy, since there has been an increase in the number of cases of resistance in areas of cultivation with irrigated rice in the state of Rio Grande do Sul (RS). In this sense, the objectives of this work were to relate the weed management practices that most interfere in grain yield (Article I), as well as to carry out a phytosociological survey of this type of plants in irrigated rice production areas in the state of RS (Article II). To this end, two studies were carried out between the years 2018 and 2019. In the study of article I, a survey was applied to 324 farmers, an instrument that provided information on the history of weed management, as well as on grain yield from their crops, located in 57 municipalities belonging to the six rice regions of the State. In the case of article II, a phytosociological survey was carried out, through the collection of soil samples in 36 farms with the cultivation of irrigated rice in the Clearfield® system, in 16 municipalities in RS. These samples were placed in polyethylene trays and arranged in a greenhouse, in order to promote the emergence of weeds, which were quantified and identified at the gender level and, subsequently, a descriptive analysis of the phytosociological parameters was performed. The answers to the survey indicate that Oryza sativa and Echinochloa spp are the most important weeds in irrigated rice crops, and the main reasons for the low control efficiency in these areas are the advanced stage of weeds and the inadequate environmental conditions. farmers who adopt crop rotation, mixing and herbicide rotation, as specific management practices, for the control of resistant weeds, obtain higher grain yields. Still, the use of pre-emergent herbicides, associated with needle-point glyphosate resulted in higher grain yield values (Article I). In the case of areas with irrigated rice cultivation in the Clearfield® system, a high weed diversity and distribution can be observed. In these places, genera Cyperus, Echinochloa, Oryza and Lolium presented the highest importance value indexes. Weed species of the Cyperus genus stand out from the others, since they have higher values for relative frequency, density and abundance, as well as a high importance value index (Article II). Thus, it was observed, with the research, that the knowledge of the agronomic practices carried out by the producers, as well as the identification of the main weed species of greater occurrence, is of fundamental importance for the recommendations of integrated measures of weed management to be efficient. , less costly and sustainable, so that they can be adopted in cultivation areas. With this, it is possible to reduce production costs and increase productivity, in order to ensure greater profitability for the irrigated rice farmer.