Weeds alter the establishment of Brachiaria brizantha cv. Marandu Malezas afectan el establecimiento de AbstractThe present study evaluated the effects of different periods of coexistence among the main weeds and Marandu brachiaria grass (Brachiaria brizantha, now Urochloa brizantha) in newly sown pasture. The experiment was conducted in a randomized block with 4 replications, with treatments being 8 coexistence periods: 0, 15, 30, 45, 60, 75, 90 and 120 days after emergence. A phytosociological assessment of the weed community was carried out at the end of the coexistence periods, and weeds were eliminated from the appropriate treatment using herbicide. Key morphogenic parameters of the forages were assessed at the end of the experimental period and dry matter production was determined. Results indicated that the presence of weeds had negative impacts on the main morphogenic components, such as plant height, number of tillers and production of leaf and stem dry matter. The presence of weeds reduced productivity in Marandu, with 15 days competition being sufficient to reduce forage production by approximately 50%, suggesting that weed control measures should be adopted within 15 days following emergence of seedlings of Marandu and weeds.Keywords: Dry matter, interference, pasture renovation, weed competition. ResumenEn un latosol localizado en Sinop, Mato Grosso, Brasil se evaluaron los efectos de la infestación de las principales malezas de la zona (Hyptis suaveolens, Senna obtusifolia y Sida rhombifolia), en diferentes edades después de la siembra, en la producción y algunas características morfogénicas de la gramínea forrajera Brachiaria brizantha (ahora: Urochloa brizantha) cv. Marandu. Los tratamientos fueron dispuestos en un delineamiento experimental de bloques al azar con 4 repeticiones y consistieron en los períodos de convivencia: 0, 15, 30, 45, 60, 75, 90 y 120 días después de la emergencia de la gramínea. Al finalizar cada uno de estos períodos se realizó una evaluación fitosociológica de la comunidad infestante y se eliminaron las malezas utilizando un herbicida. Al término del período experimental se evaluaron los principales parámetros morfogénicos del pasto, así como la producción de materia seca. Los resultados mostraron un efecto negativo de las malezas en la altura de planta y el número de rebrotes, así como en la producción de materia seca de hojas y tallos. La presencia de las malezas redujo la producción del pasto en todos los tratamientos, variando de 50% (competencia durante los primeros 15 días) hasta 74% (120 días). Por tanto las medidas de control de las malezas deben ser adoptadas durante las 2 primeras semanas de convivencia con el pasto Marandu.Palabras clave: Competencia, interferencia, materia seca, renovación de pasturas.

This research aimed at evaluating the effect of increasing coexistence periods with weeds on the nutritional components of the forage grass Brachiaria brizantha cv. Marandú under pasture renewal conditions. The experiment was arranged in randomized blocks with four replications, and treatments were represented by eight coexistence periods, namely: 0, 15, 30, 45, 60, 75, 90 and 120 days after seedling emergence. A phytosociologic evaluation was performed on the weed community at the end of the coexistence periods; later, weeds were eliminated by an herbicide formulated with aminopyralid+2,4-D (40+320 g L-1) at 2.5 L ha-1, applied in post-emergence. The fodder plants were evaluated at the end of the experimental period as for leaf-stem ratio, volumetric density of green leaf, volumetric density of total dry matter and main nutritional components, including: crude protein, neutral detergent fiber, ether extract, organic matter and mineral matter, and from this, the total carbohydrate content was calculated. The presence of weeds altered the pasture structure, since it affected negatively the leaf/stem ratio and the volumetric leaf density of B. brizantha. The coexistence also reduced the nutritional components of B. brizantha and determined that control measures should be adopted before reaching 30 days of coexistence between fodder plants and weeds.

Resumo -Este trabalho teve o objetivo de avaliar a seletividade e a eficácia da associação do glifosato com herbicidas pós-emergentes no controle de trapoeraba na cultura da soja Roundup Ready ® . Para tanto, o experimento foi instalado no delineamento de blocos ao caso, com quatro repetições, onde os tratamentos foram constituídos de quatro doses do herbicida cloransulammetil (10, 20, 30 e 40 g ha -1 ), quatro doses do herbicida clorimurom-etílico (2,5, 5,0, 7,5 e 10,0 g ha -1 ), imazetapir a 100 g ha -1 e lactofen a 72 g ha -1 , todos estes utilizados em associação com o herbicida glifosato a 960 g ha -1 . Também foram incluídas três testemunhas, sendo aplicação única do herbicida glifosato a 960 g ha -1 , aplicação sequencial do glifosato a 960/ 960 g ha -1 e testemunha geral sem capina. Os resultados demonstraram que apenas a aplicação única do herbicida glifosato a 960 g ha -1 e sua associação com as menores doses de cloransulam-metil (10 g ha -1 ) e clorimurom-etílico (2,5 g ha -1 ) não proporcionaram controle efetivo da trapoeraba. Todos os tratamentos herbicidas não influenciaram na produtividade da soja RR ® , embora a associação do glifosato com a maior dose de clorimurom-etílico (10 g ha -1 ) tenha proporcionado redução significativa no peso de 1000 grãos de soja. Palavras-chaves: soja transgênica, fitotoxicidade, seletividade, planta daninha Abstract -This research aimed to evaluate the selectivity and efficacy of glyphosate tank mixture with different post-emergent herbicides on controlling Commelina benghalensis in soybean RR ® crop. The experiment was conducted in field conditions using complete randomized block design, with four replications, where the treatments were four rates of cloransulam-methyl herbicide (10, 20, 30 and 40 g ha -1 ), four rates of chlorimuron-ethyl herbicide (2.5; 5.0; 7.5 and 10 g ha -1 ), imazethapyr at 100 g ha -1 and lactofen at 72 g ha -1 , all in association with glyphosate herbicide at 960 g ha -1 . It was also included three controls, characterized by an isolated rate of glyphosate at 960 g ha -1 , a sequential application of glyphosate at 960/ 960 g ae.ha -1 besides a check without weeds handle control. The results obtained showed that only the unique application of glyphosate herbicide at 960 g ha -1 and its association with the lower rate of cloransulam-methyl (10 g ha -1 ) or chlorimuron-ethyl (2.5 g ha -1 ) did not promote effective C.1 Recebido para publicação em 11/06/2012 e aceito em 26/01/2013.