RESUMO -A utilização intensiva do glyphosate nas lavouras de soja Roundup Ready ® (RR) no Rio Grande do Sul (RS), nos últimos anos, pode ter selecionado biótipos de leiteira (Euphorbia heterophylla) resistentes ao herbicida. Esse cenário dificultará ainda mais o manejo da espécie, já que permanecem indícios da presença de biótipos resistentes também em herbicidas inibidores da acetolactato sintase (ALS). Assim, os objetivos deste trabalho foram avaliar a sensibilidade da leiteira a herbicidas inibidores da ALS e ao glyphosate, verificar a distribuição dos biótipos resistentes no RS e determinar os principais fatores agronômicos associados a falhas de controle. Para isso, amostras de sementes de plantas de leiteira foram coletadas em lavouras de soja RR localizadas em 56 municípios do Estado do RS. Por ocasião das coletas, os agricultores responderam a questionário que abordava o manejo das plantas daninhas na área. Usando-se as sementes coletadas, foram conduzidos dois experimentos em casa de vegetação: no primeiro, avaliou-se a resposta de 86 biótipos ao herbicida glyphosate, aplicado na dose de 2.160 g e.a. ha -1 ; e, no segundo, a resposta de 73 biótipos ao herbicida imazethapyr, aplicado na dose de 200 g i.a. ha . Os resultados obtidos evidenciam que todos os biótipos de leiteira avaliados são suscetíveis ao glyphosate, porém existem biótipos resistentes aos inibidores da ALS. As respostas do questionário indicam que práticas de manejo como uso de subdoses e/ou utilização intensiva do glyphosate e a ausência de rotação de culturas favorecem falhas no controle de leiteira pelo herbicida glyphosate em soja.Palavras-chave: Glycine max, leiteira, planta daninha, suscetibilidade. ABSTRACT -The intensive use of glyphosate in Roundup Ready® (RR) soybean fields in Rio Grande do Sul (RS), in recent years may have selected wild poinsettia (Euphorbia heterophylla) biotypes resistant to the herbicide. This scenario will further complicate the management of this species, since evidence remains of the presence of herbicide resistant biotypes also in acetolactate synthase (ALS)-inhibitors. Thus, the objectives of this work were to evaluate wild poinsettia's sensitivity to the ALS-inhibiting herbicides and glyphosate; to investigate the distribution of resistant biotypes in the state of RS;and to determine the main agronomic factors associated with control failures. Seeds of wild poinsettia plants that survived glyphosate applications were collected from RR soybean fields located in 56 municipalities in the state of RS. On the occasion, the farmers were interviewed through a questionnaire aiming to collect information on the management of the area. Using the seeds collected, two experiments were conducted under greenhouse conditions. The first evaluated the response of 86 biotypes to glyphosate, applied at the rate of 2.160 g ha -1 while the second experiment evaluated the response of the herbicide imazethapyr to 73 biotypes, applied at a dose of
-Herbicide resistance can cause biochemical, physiological, morphological and phenological changes in weeds, altering their competitive ability against crops. The aim of the study was to assess physiological changes and cellular damage in susceptible and resistant biotypes of ryegrass and soybeans under competition. Three experiments were conducted in a greenhouse using a completely randomized design with four replications performed in a replacement series. The ratios of soybean and to susceptible (experiment 1) and resistant ryegrass (experiment 2) and of susceptible to resistant (experiment 3) ryegrass were 100:0, 75:25, 50:50, 25:75 and 0:100. Forty days after the emergence of the soybean crop and 60 days after the emergence of the ryegrass plants, the leaves of the competing plants were collected. The following variables were assessed: the levels of carotenoids, chlorophylls and total phenolic compounds; amount of hydrogen peroxide; degrees of lipid peroxidation and electrolyte leakage; and activity of enzymes catalase, superoxide dismutase and ascorbate peroxidase. The production of phenols and increased oxidative damage due to interspecies competition with ryegrass was, in general, observed in the soybeans; the ryegrass biotypes, susceptible and resistant to glyphosate, coexisting with soybean have generally higher oxidative damage due to intraspecific competition; since when these biotypes coexist not present modifications of these parameters.Keywords: oxidative stress, antioxidant enzymes, adaptability of herbicide resistant plants. RESUMO -A resistência aos herbicidas pode causar mudanças bioquímicas,fisiológicas, morfológicas ou fenológicas nas plantas daninhas alterando a capacidade competitiva com as culturas.O objetivo do estudo foi verificar alterações na fisiologia e os danos celulares em biótipos de azevém resistente
-Ryegrass is the main weed in wheat crop, causing yield loss due to competition by environmental resources. The objectives of this study were to estimate the fitness cost of ryegrass biotypes with low-level resistance and susceptible to fluazifop and to investigate the relative competitive ability of these biotypes between themselves and against the crop. Thus, fitness cost and competitive ability experiments were conducted under greenhouse conditions. For the fitness cost experiments, the low-level resistant ryegrass biotypes and those susceptible to fluazifop were used. For competitive ability, the treatments were arranged in a replacement series, with five proportions of the wheat cultivar FUNDACEP Horizonte and the low-level resistant and susceptible ryegrass biotypes 100:0, 75:25, 50:50, 25:75 and 0:100. Competitive analysis was carried out through diagrams applied to the replacement experiments and use of relative competitiveness indices. Variables evaluated were plant height, in the fitness cost experiment, and leaf area and shoot dry biomass in both experiments. The ryegrass biotypes show overall similar fitness cost and competitive ability. The wheat cultivar FUNDACEP Horizonte is superior in competitive ability to the ryegrass biotype with low-level resistance and equivalent to the susceptible biotype.Keywords: weed, competition, Lolium multiflorum. RESUMO -O azevém é a principal planta daninha da cultura do trigo, a qual contribui para a perda de produtividade devido à competição exercida por recursos do ambiente. Os objetivos deste trabalho foram estimar o valor adaptativo de biótipos de azevém com resistência de nível baixo e suscetível ao herbicida fluazifop e investigar a habilidade competitiva relativa desses biótipos
-Ryegrass is an annual cycle Poacea, often considered as a weed in wheat crops. The goal of this study was to analyze oxidative stress and enzyme activity of wheat and ryegrass cultures in response to stress caused by the competition between crop and weed, in two development stages. The experiment was conducted in completely randomized design, with eight replications, in replacement series, with a population of 64 plants per pot. Treatments consisted of proportions of ryegrass and wheat plants arranged in replacement series. The tested proportions were: 100/0 (pure wheat stand), 75/25, 50/50, 25/75 and 0/100% (pure ryegrass stand). The evaluated variables were: hydrogen peroxide (H 2 O 2 ) content, thiobarbituric acid-reactive species (TBARS), electrolyte leakage and activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) antioxidant enzymes. Culture and the damages caused by ryegrass competition varied according to the plant developmental stage. Both for wheat and rygrass culture, intraspecies competition caused higher oxidative stress, with increasing H 2 O 2 and TBARS contents and electrolyte leakage. SOD, CAT and APX activity increased in the culture during interspecies competition. In ryegrass, interspecies competition also increased SOD and CAT activity, whereas weed monoculture caused an increase in the APX enzyme. Generally speaking, variable behaviors were similar between the tillering and stem elongation stages. Keywords:Triticum aestivum, Lolium multiflorum, stress, competitiveness. RESUMO -O azevém é uma
-Herbicides used in Clearfield ® rice system may persist in the environment, damaging non-tolerant crops sown in succession and/or rotation. These damages vary according to soil characteristics, climate and soil management. The thickness of the soil profile may affect carryover effect; deeper soils may allow these molecules to leach, reaching areas below the roots absorption zone. The aim of this study was to evaluate the effect of the thickness of soil profile in the carryover of imazethapyr + imazapic on ryegrass and nontolerant rice, sown in succession and rotation to rice, respectively. Lysimeters of different thicknesses (15, 20, 30, 40, 50 and 65 cm) were constructed, where 1 L ha -1 of the imazethapyr + imazapic formulated mixture was applied in tolerant rice. Firstly, imidazolinone-tolerant rice was planted, followed by ryegrass and non-tolerant rice in succession and rotation, respectively. Herbicide injury, height reduction and dry weight of non-tolerant species were assessed. There was no visual symptoms of herbicide injury on ryegrass sown 128 days after the herbicide application; however it causes dry weight mass reduction of plants. The herbicides persist in the soil and cause injury in non-tolerant rice, sown 280 days after application, and the deeper the soil profile, the lower the herbicides injury on irrigated rice.Keywords: degradation, imidazolinone, Lolium multiflorum, leaching, Oryza sativa. (15, 20, 30, 40, 50 RESUMO -Os herbicidas usados na cultura do arroz
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