RESUMO:As plantas daninhas, de forma geral, causam transtornos e prejuízos para diversos agricultores.O capim-navalhão (Paspalum virgatum) tem se destacado como uma agressiva planta daninha de pastagens em diversas regiões, especialmente em áreas de solo mais úmido. A sua baixa palatabilidade, grande produção de semente, tolerância a diferentes condições de estresse ambiental, e principalmente sua semelhança morfológica, fisiológica e bioquímica com as gramíneas forrageiras dificultam seu controle. O conhecimento da capacidade germinativa das sementes de plantas daninhas pode gerar subsídios para a adoção de práticas de manejo, visando reduzir sua população em ambiente agrícola ou de criações.O presente trabalho objetivou estudar os aspectos germinativos das sementes de capim-navalhão, visando avaliar a superação de dormência de suas sementes nos seguintes tratamentos: escarificação química utilizando ácido sulfúrico (H 2 SO 4 ), por 1, 5 e 15 minutos; embebição em água em temperatura ambiente por 2, 4, 8 e 16 horas; embebição em hipoclorito de sódio por 1, 5, 10 e 15 horas; e armazenamento em temperatura elevada (40 ºC) por 0, 23, 28, 33 e 38 dias. Assim, nas condições experimentais deste estudo, o uso de escarificação química proporcionou a maior percentagem e índice de velocidade germinativa de sementes de P. virgatum, assim como o método de armazenamento em temperatura elevada (40 ºC), especificamente por 23 e 33 dias.Temperaturas elevadas, tais como ocorrem no solo podem contribuir para a quebra de dormência das sementes capim-navalhão, assemelhando-se ao ato dos ruminantes ao se alimentarem das partes da gramínea, passando pelo trato digestivo,que possui efeito semelhante ao do ácido sulfúrico, contribuindo assim para que ocorra a quebra de dormência e,posteriormente disseminam as sementes da espécie. Palavras chave: Paspalum virgatum.planta daninha.Germinação.temperatura elevada.hipoclorito de sódio.

The use of herbicides such as 2,4-D + picloram in livestock areas can contaminate and hinder the use of the production system for subsequent crops of other crops. The objective of the research was to evaluate the ability of landrace maize varieties to reduce contamination of soil treated with 2,4-D + picloram, simulating existing conditions in the Amazon Biome. The experiment consisted of 6 phytoremediation treatments (4 landrace maize varieties, 1 hybrid maize cultivar and 1 control without cultivation), 2 herbicide conditions (with and without) and 3 evaluation periods (28, 56 and 84 days). The soil was contaminated and the maize was subsequently cultivated under the herbicide conditions mentioned above. After each evaluation period, soil samples were collected, which were used to mount bioassays by growing cucumber (plants sensitive to the herbicide). Emergence, aerial dry mass and root dry mass were evaluated. All variables were affected by the herbicide residue. However, the reduction in herbicide persistence in each evaluation period was notable, resulting in the normal reestablishment of bioindicator seedlings, especially in the last evaluation at 84 days. The samples obtained in the soil cultivated with the varieties CR purple and CR white showed the best conditions for the development of cucumber, demonstrating the potential to be studied in phytoremediation programs.

The presence of weeds amid pastures has caused significant damage to cattle farmers due to the difficulty in controlling these species. Paspalum virgatum stands out as an aggressive weed in Amazonian agroecosystems. Proper management of weed species is threatened by their aggressiveness, adaptation to low fertility soils and morphological, physiological and biochemical similarities with the grasses used as fodder. It is also possible that part of these characteristics of aggressiveness occur due to the ability of weeds to produce allelochemicals, resulting in damage to surrounding plants. The objective of this study was to qualitatively verify the presence of secondary metabolites in P. virgatum species under different water availability. The analyzed species were initially grown separately under three conditions of water availability: water deficit, field capacity and flooded environment. The water deficit treatment was conducted to verify weed ability to develop under conditions of extreme water shortage. This is a characteristic related to its rusticity, as found in grasses in the Amazon region. Excess water treatments were also conducted, since this is a common condition found in areas with partial flooding of a few months during the rainy season in the Amazon. After 120 days, weeds were collected and separated into roots, stems and leaves. The material was subsequently dried, ground and subjected to procedures to determine secondary metabolites. Phenolic compounds, flavonoids and alkaloids were identified in all conditions of plant development. The flavonoid detection test presented an intense yellow color. This is a strong indication of the presence of this class in stems and leaves of plants under flood and in leaves of plants under field capacity soil conditions. An intense presence of phenolic compounds was verified in stems and leaves, regardless of treatment. General alkaloids were found in great intensity in all samples. Saponins were found in leaves of P. virgatum under water stress (flooding and water deficit). All the metabolites were found in the plants, diverging between treatments and parts of the plant. It was concluded that the species presented higher steroid content in the roots when growing in places with excess of water. In conditions of full water supply, the presence of steroid was less intense in the roots, leaves and stems, result also found in roots and leaves of plants under water deficit. Alkaloids were less intensely present in the roots, regardless of the water treatment in which the plant was submitted. Results demonstrated that there are secondary metabolites responsible for some physiological ability of the weed to withstand excess or water deficit, indicating the need for further studies

RESUMO: O sucesso da produção pecuária brasileira está estreitamente relacionado com a manutenção adequada das pastagens. Pastagens degradadas pela presença de plantas daninhas constituem se, atualmente, em um dos maiores problemas desse setor, reduzindo a produtividade e a qualidade da forrageira. Objetivou-se, neste trabalho verificar a ação de subdoses de herbicidas no controle da planta daninha "malva" em área de pastagem. O delineamento experimental foi em blocos casualizados, com 10 tratamentos distribuídos em esquema fatorial (2 x 5), sendo 2 herbicidas aplicados em 5 doses: 2,4-D e a formulação 2,4-D+picloram, em: 0; 3; 6; 12,5 e 25% da dose recomendada para controle de plantas daninhas em culturas perenes (4,0 L ha-1). Foram realizadas avaliações de controle na malva e determinação da altura das plantas aos 7; 14; 21 e 28 dias após a aplicação, além da fitointoxicação no capim braquiária nas mesmas datas de avaliação. Não houve sintoma de fitointoxicação na forrageira. Controle igual ou superior a 90% de malva foi verificado a partir das doses de 12,5% da dose recomendada de 2,4-D+picloram e 25% de 2,4-D. Os herbicidas foram eficientes no controle da espécie, mesmo em doses inferiores ao recomendado para espécies de difícil controle.