Resumo -As principais plantas daninhas encontradas na cultura do trigo são o nabo e o azevém, e seu controle em pós-emergência é baseado em herbicidas inibidores da enzima acetolactato sintase (ALS) e acetil coenzima A carboxilase (ACCase) que, em função da resistência, limita as opções de controle. Associações de herbicidas têm sido utilizadas em pós-emergência do trigo, porém, seus efeitos na cultura são pouco conhecidos. O objetivo deste trabalho foi avaliar a seletividade de associações de herbicidas e doses aplicados em pós-emergência do trigo. Foram realizados três experimentos a campo em sistema de semeadura direta, no delineamento de blocos ao acaso com três repetições. Os experimentos foram conduzidos nos municípios de Santa Bárbara do Sul-RS, Cruz Alta-RS e Tupanciretã-RS. Foram estudadas doses e associações entre os herbicidas 2,4-D, metsulfuron-methyl, iodosulfuron, piroxsulam e saflufenacil aplicados no perfilhamento do trigo. As variáveis avaliadas foram fitotoxicidade aos sete, 14, 21 e 35 dias após a aplicação (DAA), rendimento de grãos (kg ha -1 ) e peso hectolitro dos grãos de trigo (PH), sendo os dados dos três experimentos analisados de forma conjunta. Aos 35 DAA as maiores fitotoxicidades foram observadas para metsulfuron-methyl na dose de 9 g i.a. ha -1 e para saflufenacil associado ao metsulfuron-methyl. Os resultados de rendimento de grãos demonstraram que a associação entre 2,4-D e metsulfuron-methyl, saflufenacil isolado ou associado à metsulfuron-methyl e o iodosulfuron-methyl foram seletivos para o trigo. O aumento da dose de metsulfuron-methyl (6 e 9 g i.a. ha -1 ) e a dose de registro de piroxsulam causaram redução significativa na rendimento de grãos de grãos de trigo na média dos três experimentos. O PH dos grãos de trigo não foi influenciado pelos herbicidas estudados. Palavras-chave: Triticum aestivum, mistura de herbicidas, mistura em tanque, resistência Abstract -The main weeds in wheat are wild radish and ryegrass, and its post-emergence control is based on herbicides inhibiting the enzyme acetolactate synthase (ALS) and acetyl coenzyme A carboxase (ACCase), which as a function of resistance limits the control options. Herbicide combinations have been used for post-emergence of wheat; however, the effects of herbicidal combinations are poorly understood. The objective of this work was to evaluate the selectivity of Piasecki et al. Rev. Bras. Herb., v.16, n.4, p.286-295, out./dez. 2017 287
Ryegrass is an important weed in wheat cultivations due to the evolution of resistance to different mechanisms of action. This study aimed to compare the phenological development, fitness cost, and competitive ability between ryegrass biotypes susceptible and with multiple resistance to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and acetolactate synthase (ALS) inhibiting herbicides. Fitness cost and phenological development were evaluated from biotypes grown in pots, and morphological growth variables were determined up to 140 days after emergence. Phenological development was evaluated with a fitness cost. Competitive ability was determined in a replacement-series experiment with proportions of resistant and susceptible ryegrass. The tested proportions were 100:0 (pure resistant ryegrass stand), 75:25, 50:50, 25:75, and 0:100% (pure susceptible ryegrass stand), where the number of tillers, height, leaf area, and shoot dry matter were evaluated at 50 days after emergence. The longer tillering period of resistant ryegrass was the main factor involved in the difference in phenological development between biotypes. The resistant biotype was superior to the susceptible regarding height, shoot dry matter, and absolute growth rate, while the susceptible biotype had a higher number of tillers and leaf area ratio. Thus, the resistant biotype had no fitness cost. For competitive ability, no difference was observed between biotypes in the different tested proportions when they occupied the same ecological niche.
The intergenotypic competition of tetraploid ryegrass with natural diploid population may be a tool to reduce the frequency of resistant individuals in an area. This study aimed to identify and compare the phenological development, fitness cost, and competitive ability between diploid and tetraploid ryegrass genotypes. Genotypes were grown in pots, and the morphological variables of genotype growth were assessed every 15 days up to 120 days after emergence to evaluate the fitness cost. Phenological development and seed yield components were measured in a single time together with the fitness cost. Competitive ability was determined in a replacement-series experiment with proportions of tetraploid and diploid ryegrass, in which the number of tillers, plant height, leaf area, and shoot dry weight were assessed at 50 days after emergence. The results of fitness cost showed that the number of tillers, leaf area, root dry weight, and the number of seeds were higher for tetraploid ryegrass, which presented a higher competitive ability than the diploid genotype regardless of the tested proportions. Tetraploid ryegrass may be useful for reducing the frequency of herbicide-resistant diploid ryegrass because of its higher competitive potential.
Resistance to herbicides is one of the main factors responsible for weed control failures. Once uncontrolled and stressed, resistant weeds demand a new application of herbicides from different modes of action, which results in higher monetary costs and environmental impact. Knowledge of weed sensitivity levels to herbicides before making decisions for their management in the field is paramount to increasing the efficiency of integrated weed management. Thus, methods that allow the rapid determination of sensitivity levels can help to the correct recommendation before the application, and thus, favor the greater technical, economic and environmental efficiency of weed management. The objective of this work was to validate a rapid method to detect the levels of sensitivity of black picker (Bidens pilosa) and horseweed (Conyza sumatrensis) to saflufenacil. Dose-response experiments were performed in growth chamber, greenhouse and field. The control provided by different doses of the saflufenacil herbicide was evaluated in each environment, and the results correlated within each species. The results showed a significant positive correlation for the results obtained in growth chamber and greenhouse for black picker and horseweed. These results indicate that the method developed in the growth chamber can replace greenhouse tests for determination of the sensitivity of black picker and horseweed to saflufenacil.
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