RESUMO O milho é um dos principais cereais cultivados no mundo e o leiteiro aparece entre as plantas daninhas que causam prejuízos na produção de grãos. Objetivou-se com o trabalho avaliar a habilidade competitiva relativa de híbridos de milho na presença de um biótipo de leiteiro, por meio de experimentos em série de substituição. Em experimentos preliminares, determinou-se a população de plantas em que a massa seca se torna constante. Tanto para os híbridos de milho Agroeste, Morgan, Nidera e Velox, quanto para o leiteiro, a população foi de 20 indivíduos vaso-1. Posteriormente foram instalados experimentos conduzidos em série de substituição, nas diferentes combinações das espécies, variando-se as proporções relativas (100:0, 75:25, 50:50, 25:75 e 0:100%). A análise da competitividade das espécies foi efetuada por meio de diagramas aplicados a experimentos substitutivos e pelos índices de competitividade relativa. A estatura (EP), índice de clorofila (IC), área foliar (AF) e a massa seca da parte aérea (MS) das plantas foram avaliadas aos 50 dias após a emergência. Ocorre competição entre os híbridos de milho com o leiteiro, sendo ambos afetados negativamente, independentemente da proporção de plantas, provocando reduções nas EP, IC, AF e MS das espécies. A competição entre o milho e leiteiro ocorre basicamente pelos mesmos recursos do meio. A competição interespecífica ocasiona maiores prejuízos ao milho e o leiteiro do que a competição intraespecífica. De modo geral observou-se que apenas os híbridos Nidera e Velox foram mais competitivos do que o leiteiro.

ABSTRACT Maize is one of the main cereals cultivated worldwide and wild poinsettia is among the weeds that cause damage in grain production. The objective of this study was to evaluate the relative competitive ability of maize hybrids in the presence of a wild poinsettia biotype through experiments in replacement series. In preliminary experiments, it was determined the plant population in which the dry mass becomes constant. For the maize hybrids ‘Agroeste’, ‘Morgan’, ‘Nidera’, and ‘Velox’, as well as the wild poinsettia, the population was 20 individuals vase-1. Subsequently, experiments were carried out in replacement series in different combinations of species that varied the relative proportions (100:0, 75:25, 50:50, 25:75, and 0:100%). The analysis of the species' competitiveness was carried out using diagrams applied to the replacement experiments and by the relative competitiveness indexes. The height (PH), chlorophyll index (CI), leaf area (LA), and the shoot dry mass (DM) of the plants were evaluated 50 days after emergence. There was competition between the maize hybrids and the wild poinsettia; both were negatively affected, regardless of the proportion of plants, causing reductions in the species' PH, CI, LA, and DM. The competition between maize and wild poinsettia occurs for the same resources in the environment, and interspecific competition caused greater damage to maize and wild poinsettia than intraspecific competition. In general, it was observed that only the hybrids ‘Nidera’ and ‘Velox’ were more competitive than the wild poinsettia.

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.

Resumo: O objetivo deste trabalho foi avaliar a densidade e a composição do banco de sementes de plantas daninhas do solo ao se cultivar feijão, milho e soja no sistema plantio direto (SPD), em rotação com espécies de cobertura de inverno, e no sistema plantio convencional (SPC). O experimento foi instalado em campo, em delineamento de blocos ao acaso, com três repetições. A contagem do banco de sementes foi realizada em amostras de solo (0-10 e 10-20 cm) em quatro pontos de cada unidade experimental, aos 15, 30, 60 e 90 dias de cultivo. As culturas de feijão, milho e soja foram semeadas no SPD com diferentes coberturas vegetais do solo em rotação, bem como no SPC. O SPD proporcionou banco de sementes do solo com maior densidade e abundância das espécies Gnaphalium spicatum e Oxalis corniculata com o cultivo de milho, soja e feijão. A espécie Lolium multiflorum teve menor densidade e menos sementes no banco do solo ao se adotar o SPD. O uso das coberturas de inverno aveia-preta e ervilhaca, em cultivo isolado ou em consórcio, proporcionou menor densidade de espécies de plantas daninhas, em especial de L. multiflorum. O SPD proporciona menor densidade de espécies de plantas daninhas no banco de sementes do solo que o SPC.

Abstract: The objective of this work was to evaluate the density and composition of the soil weed seed bank when bean, corn, and soybean are cultivated in the no-tillage system (NTS) in rotation with winter cover crop species and in the conventional tillage system (CTS). The experiment was installed in a complete randomized block design with three replicates. The evaluation of the seed bank was performed on soil samples (0-10 and 10-20 cm) in four points of each experimental unit, at 15, 30, 60, and 90 days of cultivation. Bean, corn, and soybean crops were sown in the NTS with different soil cover crops in rotation, as well as in the CTS. The NTS provided a more dense and abundant soil seed bank of the species Gnaphalium spicatum and Oxalis corniculata when corn, soybean, and bean were cultivated. The species Lolium multiflorum showed lower density and less seeds in the soil seed bank when the NTS was adopted. The use of the winter cover crops black oat and cow vetch, cultivated individually or in consortium, resulted in a lower density of weed species, especially of L. multiflorum. The NTS provides a lower density of weed species in the soil seed bank than the CTS.