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Biotic and abiotic factors such as competition with weeds and water deficit may cause significant losses to soybean productivity. This study aimed at evaluating the effect of water deficit and plant recovery in the interaction between soybean (Glycine max) and slender amaranth (Amaranthus viridis) by using growth variables. A replacement series experiment was performed and treatments were arranged in a factorial scheme; they were composed of two water regimes (field capacity and water deficit (50% of field capacity)) and different soybean and slender amaranth proportions (100:0, 50:50 and 0:100%). Water regimes were applied 20 days after plant transplant. Height, leaf area and shoot dry matter were evaluated in soybean and slender amaranth under field capacity and water deficit, returning to normal irrigation conditions to evaluate the water recovery. Soybean exhibited competitiveness which was equivalent to the slender amaranth, independent of the water regime. Water deficit negatively influenced height, leaf area and shoot dry matter of soybean and slender amaranth. There was a reduction in leaf area and shoot dry matter of soybean after plant recovery caused by the irrigation deficit period. [ABSTRACT FROM AUTHOR]

The awareness of agronomic practices that affect the resistance selection of weeds to a particular herbicide is of utmost importance in order to advocate management practices that aim to avoid or prolong the resistance. The objectives of this study were to identify and map the occurrence of the wild poinsettia's low-level resistance to glyphosate in Rio Grande do Sul State (RS), Brazil, and to define the main agronomic factors associated with the selection of these biotypes. Seed and / or soil samples in areas with suspected resistance were collected in Roundup Ready® (RR) soybean crops in different counties in the RS region during the 2010/11 and 2011/12 seasons. A questionnaire on the operations history in the area was applied at each site in order to establish relationships between the distribution of wild poinsettia with cases of suspected resistance to glyphosate and the likely agronomic factors involved in this occurrence. The study included the response of wild poinsettia biotypes with suspected resistance to glyphosate and an analysis of the questionnaires carried out with producers. The main agronomic practices used by producers that favor the emergence of resistant biotypes were the continued cultivation of the RR® soybean; an overdependence on the use of glyphosate; a low rate of crop rotation and efficient chemical alternatives for wild poinsettia control and management. [ABSTRACT FROM AUTHOR]

The genus Digitaria has a great ecological adaptability, being exceptionally harmful to maize crops. Appropriate management practices are necessary to reduce the negative effects of this weed and avoid maize yield losses. The effects of different cover crops straw levels, when incorporated or maintained on the soil surface, on the initial development of Digitaria spp. (crabgrass) were evaluated. The experimental design used consisted of randomized blocks, with four replications. Treatments were arranged in factorial scheme with the following factors: (A) - cover crops management (incorporated and on the soil surface), (B) - cover crops (Brassica napus, Raphanus sativus, Trifolium vesiculosum and Lolium multiflorum, and (C) - straw levels (0, 1, 2, 4, 6 and 10 t ha-1). At least 6 t ha-1 of straw were needed on the soil surface to reduce crabgrass growth. Lolium multiflorum straw provided, in general, greater reduction in the growth parameters of Digitaria spp. As the cover crops straw levels increased on the soil surface, a reduction of Digitaria spp. growth was observed. [ABSTRACT FROM AUTHOR]

The chemical substances released by plant residues left on soil surface have different behaviors from the incorporation. The aim of this study was to investigate the effects of different levels of cover crops straws, when incorporated or maintained on the soil surface, on the emergence of Digitaria spp. (crabgrass). The experimental design was randomized blocks with four replications. Treatments were arranged in a factorial scheme with the following factors: (A) - cover management (incorporated and on the soil surface), (B) - cover crops (Brassica napus, Raphanus sativus, Trifolium vesiculosum and Lolium multiflorum) and (C) - straw levels (0, 1, 2, 4, 6 and 10 t ha-1). The Digitaria spp. emergence rates were favored by the increasing levels of straw on the soil surface. With increasing levels of cover crop straws incorporated into the soil a tendency on the reduction of Digitaria spp. emergence was observed. The cover crops had little influence on reducing the emergence of Digitaria spp. [ABSTRACT FROM AUTHOR]

The incidence of volunteer Enlist™ soybean in the post-emergence of crops in succession, such as wheat, requires changes in chemical control. Thus, the objective of the work is to evaluate the efficiency of different post-emergence herbicides in the control of volunteer Enlist™ soybean and wild radish and their selectivity to wheat. For this, four experiments were conducted in 2017 and 2018 in field and greenhouse. The treatments tested were pyroxsulam, saflufenacil, pyroxsulam + saflufenacil, pyroxsulam + bentazon, pyroxsulam + metribuzin, saflufenacil + bentazon, and saflufenacil + metribuzin in 2017, and triclopyr, saflufenacil, MCPA, quinclorac, dicamba, pyroxsulam + metribuzin, metribuzin + metsulfuron, pyroxsulam + bentazon and bentazon + metsulfuron in 2018. The variables were the control of wild radish and volunteer Enlist™ soybean phytotoxicity to wheat crop, yield components, and yield total. The association of the herbicides pyroxsulam and saflufenacil is efficient in the management of volunteer soybean EnlistTM, showing selectivity to wheat. The isolated application of dicamba and the associations of pyroxsulam with metribuzin and metribuzin with metsulfuron represent alternatives for selective management of volunteer Enlist™ soybean in wheat, in addition to efficiently controlling wild radish in post-emergence. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine changes in the photosynthetic process and the inhibition of 5-enolpyruvylshikimate-3- phosphate synthase (EPSPs) by shikimic acid accumulation, after application of the herbicide glyphosate in four biotypes of C. sumatrensis collected in the state of Rio Grande do Sul. Therefore, the experiments were conducted under greenhouse and laboratory, assessing plant biomass, photosynthesis rate, transpiration and water use efficiency; the amount of shikimic acid was calculated for each treatment. Glyphosate application reduced growth and affected the photosynthesis rate and water use efficiency of the biotypes differentially, and the resistant biotype had small interference from glyphosate, while physiological parameters of the susceptible biotype were deeply affected by the herbicide. Susceptible biotypes had higher shikimic acid accumulation than the resistant biotype, indicating differential sensitivity of EPSPs to glyphosate between resistant and sensitive biotypes. [ABSTRACT FROM AUTHOR]