RESUMEN Entre las malezas que interfieren en el crecimiento y desarrollo del sorgo dulce se destaca el amor seco, especialmente por presentar alta capacidad competitiva por los recursos disponibles en el medio. El objetivo de este estudio es comparar la capacidad competitiva del sorgo dulce (Sorghum bicolor) frente al papunga (Bidens pilosa), en función de la proporción de cultivo y planta. Los experimentos se realizaron en un invernadero en un diseño completamente al azar, con cuatro repeticiones. Los tratamientos se organizaron en series de reemplazo en las proporciones de 100: 0, 75:25, 50:50, 25:75 y 0: 100% (sorgo: maleza) que correspondieron a 20:0, 15:5, 10:10, 5:15 y 0:20 plantas por maceta con volumen de 8 dm3 de sorgo dulce (cultivares BRS 506, BRS 509 o BRS 511) contra B. pilosa. Cincuenta días después de la emergencia, se evaluaron el área foliar de la planta (LA), la masa seca de los brotes (MS), la fotosíntesis (A) y la transpiración (E). La capacidad competitiva se analizó utilizando el método de análisis gráfico, construyendo diagramas basados en la productividad total y relativa. También se determinaron la competitividad, el coeficiente de agrupamiento y la agresividad. Los cultivares de sorgo, en general, fueron menos competitivos en todas las proporciones de B. pilosa. Hubo pequeñas diferencias en la capacidad competitiva entre los cultivares de sorgo; BRS 509 demostró ser ligeramente más competitivo que BRS 506 y BRS 511 frente al B. pilosa a. Sin embargo, es poco probable que esto proporcione una ventaja competitiva para BRS 509 en los campos de producción, por lo que B. pilosa a debe controlarse de manera eficiente al principio del ciclo de cultivo para evitar pérdidas de productividad, independientemente del cultivar de sorgo.

ABSTRACT Among the weeds that interfere with the growth and development of sweet sorghum, beggar ticks stands out, because it has a high competitive capacity for the available resources. This study aims to compare the competitive ability of sweet sorghum (Sorghum bicolor (L.) Moench) against hairy beggarticks (Bidens pilosa L.), as a function of cultivar and plant proportion. Experiments were conducted in a greenhouse in a completely randomized design with four replications and six treatments. Treatments were arranged in replacement series in the proportions of 100:0, 75:25, 50:50, 25:75, and 0:100% (sorghum:weed) equivalent to 20:0, 15:5, 10:10, 5:15 and 0:20 plants per pot with 8 dm3 capacity of sweet sorghum (cultivars ‘BRS 506’, ‘BRS 509’ or ‘BRS 511’) against hairy beggarticks. Fifty days after emergence, plant leaf area (LA), aboveground dry mass (DM), photosynthesis (A), and transpiration rates (E) were measured. Competitive ability was analyzed by using the graphical analysis method and building diagrams based on total and relative productivity. Competitiveness, clustering coefficient, and aggressiveness were also determined. Sorghum cultivars, in general, showed losses independently of the proportion of hairy beggarticks. Statistical analysis showed small differences in competitive ability among sorghum cultivars; ‘BRS 509’ was also demonstrated to be slightly more competitive than ‘BRS 506’ and ‘BRS 511’ against hairy beggarticks. This, however, is unlikely to provide a competitive advantage for ‘BRS 509’ in production fields, and hairy beggarticks should be efficiently controlled early in the crop cycle to avoid productivity losses, independently of the sorghum cultivar.

ABSTRACT The study of weed interference periods and the economic threshold level (ETL) of weeds on crops allows the adoption of management methods and the rationalized use of herbicides. The objective of this study was to determine the periods of interference and to test mathematical models to determine the economic threshold level of ryegrass in the wheat crop. Two experiments were carried out in a randomized block design with four replications. The first experiment was conducted in the 2014/2015 agricultural season. The periods of interference and control of ryegrass were studied in wheat. The periods of interference and/or control were: 0, 10, 20, 30, 40, 50 and 120 days after emergence (DAE). The second experiment was conducted in the 2016/2017 agricultural season. The ETLs were studied, being the treatments composed of wheat cultivars and 12 populations of ryegrass, in competition with the respective cultivars. The results allowed concluding that the management methods of weed ryegrass must be adopted in the period between 11 and 21 days after crop emergence, which is described as a critical period of control of this weed. The wheat grain yield loss competing with ryegrass reached 59% when grown with ryegrass. For ETL, the linear regression model of the rectangular hyperbola adequately estimates grain yield losses in the presence of ryegrass. The cultivar presenting the lowest values of ETL, that is, less capacity to live with the weed, was TBIO Alvorada. The other cultivars presented similar ETL values.

RESUMO A identificação da habilidade competitiva de híbridos de milho e do nível de dano econômico (NDE) ocasionado pelo papuã (Urochloa plantaginea) torna-se importante para a adoção do manejo integrado dessa planta daninha. Diante disso, objetivou-se com este trabalho avaliar a interferência e o NDE de papuã infestante de híbridos de milho. Os tratamentos foram compostos pelos híbridos de milho Syngenta Status VIP 3, Syngenta SX8394 VIP 3, Pioneer P1630H, Pioneer 30F53 YH e Dow 135021 e 12 densidades de plantas de papuã para cada híbrido. Para descrever a relação entre a perda de produtividade de grãos do milho e as variáveis explicativas densidade de plantas (DP), massa seca da parte aérea (MS), cobertura do solo (CS) e área foliar (AF), usou-se o modelo da hipérbole retangular. A determinação do NDE foi efetuada usando-se a produtividade de grãos, custo de controle, preço do milho e eficiência do herbicida. O modelo da hipérbole retangular estima de modo satisfatório as perdas de produtividade de grãos em função da interferência do papuã na cultura do milho. Os híbridos Pionner 30F53 YH e Pionner P1630H apresentaram melhor competitividade e os maiores NDEs. A semeadura dos híbridos Pioneer P1630H, Pioneer 30F53 YH e Dow 135021 aumenta o NDE, justificando a adoção de medidas de controle em densidades mais elevadas.

ABSTRACT Identifying the competitive ability of corn hybrids and the economic injury level (EIL) caused by Urochloa plantaginea is important for the adoption of integrated management of this weed. This work aims to evaluate the interference and EIL of U. plantaginea infesting corn hybrids. Treatments included the corn hybrids Syngenta Status VIP3, Syngenta SX8394 VIP3, Pioneer P1630H, Pioneer 30F53 YH, and Dow 135021, as well as 12 densities of U. plantaginea for each hybrid. We used a rectangular hyperbolic model to describe the relationship between corn grain productivity loss and the explanatory variables — plant density (PD), dry mass (DM) of the aerial parts, ground cover (GC), and leaf area (LA). EIL was determined using grain productivity, control cost, corn price, and herbicide efficacy. The rectangular hyperbolic model provides a satisfactory estimate of grain productivity loss regarding the interference of U. plantaginea in corn culture. The hybrids Pioneer 30F53 YH and Pioneer P1630H presented better competitiveness and higher EIL. Sowing the hybrids Pioneer P1630H, Pioneer 30F53 YH, and Dow 135021 increased EIL, justifying the adoption of control measures for U. plantaginea at higher densities.