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Paraguaçu Paulista, Brazil

Silva A.A.,Federal University of Vicosa | Lima C.F.,Dep. de Quimica | Queiroz M.E.L.R.,Dep. de Quimica | Franca A.C.,Federal University of Vales do Jequitinhonha and Mucuri | D'antonino L.,Dep. de Fitotecnia
Planta Daninha | Year: 2010

The objective of this study was to determine the half-life (t1/2) for the herbicide ametryn in Red-Yellow Latosol (LVA) and Red-Yellow Ultisol (PVA) with different pH values. Thus, plastic pots coated inside with plastic film were filled with 330 g of samples from the soils under study (LVA with pH values adjusted to 4.4, 4.9 and 5.8, and PVA pH 5.9), collected in degraded pastures without herbicide application. Ametryn was applied on these soil samples at a dose of 5.0 ha L-1. Twelve hours after application, the first soil samples were extracted from the pots to determine the concentration at zero time, and every five days new samples were removed from the other pots (two per time) to determine ametryn concentration over time. Ametryn extraction from the soil matrix was performed by Solid Liquid Extraction with Partition at Low Temperature (SLE-PLT) and quantified by liquid chromatography. A biological test for indirect determination of herbicide persistence was also carried out. Results indicated that ametryn half-life (t1/2) on the soils evaluated was 26, 19, 12 and 11 days in LVA soil pH 4.4; pH 4.9; pH 5.8 and PVA pH 5.9, respectively. Both methods (chromatography or bioassay) used to evaluate ametryn persistence in soils showed that degradation of this herbicide is strongly influenced by soil pH and organic matter content.

Melo C.A.D.,DFT UFV | Medeiros W.N.,DFT UFV | Tuffi Santos L.D.,Federal University of Minas Gerais | Ferreira F.A.,Dep. de Fitotecnia | And 2 more authors.
Planta Daninha | Year: 2010

The aim of this study was to evaluate herbicide leaching in three soil profiles. Doses of 0.50 and 0.75 kg ha-1 sulfentrazone, 0.113 and 0.169 kg ha-1 isoxaflutole, and 0.72 and 1.08 kg ha-1 oxyfluorfen were applied on the surface of 30 cm high PVC columns filled with the three soil following types: one with a sandy loam texture and two clayey ones with low and high organic matter contents. After applying these herbicides, the columns were submitted to two rounds of 40 mm-simulated rain with a 24h interval between them. Herbicide leaching was detected by bioassay method using sorghum (Sorghum bicolor) plants. Both the activity and movement of the herbicide sulfentrazone in the soil profile increased after application of the highest dose. After application of 0.75 kg ha-1 of sulfentrazone, the highest downward movement was observed in the sandy loam soil, down to 27.5 cm, followed by the clayey soils with low and high organic matter contents, down to 25.0 and 17.5 cm, respectively. A high leaching potential was observed of isoxaflutole, which exceeded 22.5 cm in depth for the three soils and both doses studied. However, oxyfluorfen remained adsorbed in surface layers of soil only. When comparing the types of soil, the highest herbicide activity and movement occurred in the sandy loam soil. soxaflutole presented greater mobility than sulfentrazone, while oxyfluorfen showed low leaching potential.

Franca A.C.,Federal University of Vales do Jequitinhonha and Mucuri | Freitas M.A.M.,Federal University of Vicosa | Fialho C.M.T.,Federal University of Vicosa | Silva A.A.,Dep. de Fitotecnia | And 3 more authors.
Planta Daninha | Year: 2010

This study evaluated the effects of glyphosate on the growth of three arabica coffee cultivars. A factorial (3 × 5) was arranged in a randomized block design with four replications, with treatments consisting of three coffee varieties: Catucaí Amarelo (2 SL), Oeiras (MG-6851) and Topázio (MG-1190) and five glyphosate doses (0, 57.6, 115.2, 230.4 and 460.8 g ha-1). The herbicide was applied when the coffee plants reached 21 pairs of leaves, before reaching their upper third ones. At 45 and 120 days after glyphosate application (DAA), increase in leaf area, stem diameter, number of leaves and plagiotropic branches was evaluated, being initially measured on the day the herbicide was applied, and plant intoxication rate at 10, 45 and 120 DAA. Dry matter of leaves, roots and stem, and root length and density were measured at 120 DAA. Symptoms of coffee plant intoxication caused by glyphosate were similar in different cultivars, being characterized by chlorosis and leaf narrowing. Increase in the number of leaves, plagiotropic branches and stem diameter, regardless of the cultivar, was not affected by glyphosate. Cultivar Topázio was the most sensitive to glyphosate, in terms of accumulation of leaf area, root dry matter and root density.

Albuquerque J.A.A.,Dep. de Fitotecnia | Melo V.F.,Dep. de Solos e Engineering Agricola | Siqueira R.H.S.,UFRR | Martins S.A.,UFRR | And 3 more authors.
Planta Daninha | Year: 2012

The aim of this work was to identify the occurrence of weeds after five years of notillage corn cultivation in the Amazonian savannah. A phytosociological survey was conducted involving collection, identification, and quantification of the weeds, after corn harvest during June and July, 2010. The investigated properties included botanical classes, families, species, number of individuals, frequency, density, abundance, relative frequency, relative density, relative abundance, importance value index, propagation method, and life cycle. The emergent vegetation in the study area had 419 species, nine of which were identified as Dicotyledons, while six were identified as Monocotyledons. Species in the Ciperaceae family were the most abundant, while the families Poaceae, Ciperaceae, Asteraceae, Malvaceae, and Fabaceae exhibited the highest number of individuals and species frequency per plot. Only the Cordia curassavica shrubby growth habit was identified. Cyperus rotundus species showed the highest values in all the phytosociological parameters evaluated, with an importance index value 1.5 times higher than that of Brachiaria humidicola which had the second highest value (40.49).

Tavares S.S.,Federal University of Alagoas | Tavares S.S.,Federal University of Vicosa | Ramos-Sobrinho R.,Federal University of Vicosa | Gonzalez-Aguilera J.,Dep. de Fitotecnia | And 3 more authors.
Planta Daninha | Year: 2012

Begomoviruses are whitefly-transmitted, single-stranded DNA viruses that are often associated with weed plants. The aim of this study was to further characterize the diversity of begomoviruses infecting weeds (mostly Sida spp.) in Brazil. Total DNA was extracted from weed samples collected in Viçosa (Minas Gerais state) and in some municipalities of Alagoas state in 2009 and 2010. Viral genomes were amplified by RCA, cloned and sequenced. A total of 26 DNA-A clones were obtained. Sequence analysis indicated the presence of 10 begomoviruses. All viral isolates from Blainvillea rhomboidea belonged to the same species, Blainvillea yellow spot virus (BlYSV), thereby suggesting that BlYSV may be the only begomovirus present in this weed species. Four isolates represent new species, for which the following names are proposed: Sida yellow blotch virus (SiYBV), Sida yellow net virus (SiYNV), Sida mottle Alagoas virus (SiMoAV) and Sida yellow mosaic Alagoas virus (SiYMAV). Recombination events were detected among the SiYBV isolates and in the SiYNV isolate. These results constitute further evidence of the high species diversity of begomoviruses in Sida spp. However, the role of this weed species as a source of begomoviruses infecting crop plants remains to be determined.

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