Respiration induced by substrate and bacteria diversity after application of diuron, hexazinone, and sulfometuron-methyl alone and in mixture.

After application, herbicides often reach the soil and affect non-target soil microorganisms, decreasing their population, diversity or affecting metabolic activity. Therefore, laboratory studies were performed to evaluate the effects of diuron, hexazinone and sulfometuron-methyl alone and mixed upon carbon transformation by soil microorganisms in clayey and sandy soils and the effect on bacterial diversity and structure. Control treatment without herbicide application was also performed. Sub-samples from the control and herbicide treatments (10 g - in triplicate) were collected before herbicide application and 7, 14, 28 and 42 days after treatment (DAT), then 1 mL of 14C-glucose solution was applied. The released 14CO2 was trapped in 2 M NaOH solution and the radioactivity was analyzed by liquid scintillation counting (LSC), 12 h after glucose application. The effect of herbicides on bacterial diversity was evaluated by T-RFLP. The experiment was conducted in a complete randomized design. Hexazinone did not affect 14CO2 evolution. Diuron showed a greater 14CO2 evolution in sandy and clayey soil, while sulfometuron-methyl led to an increase in sandy soil, at 42 DAT. A greater evolution of carbon was observed in the treatment with herbicide mixture in sandy soil, compared with the same treatment in clayey soil or control. However, the herbicide mixture application did not affect the soil biological activity measured by the respiration rate induced by substrate. On the other hand, the herbicide mixtures affected the bacterial diversity in both soils, being the strongest effect to diuron and sulfometuron-methyl in clayey soil and hexazinone in sandy soil.

Absorption and translocation of sulfometuron-methyl in sugarcane (Saccharum officinarum L.) at different growth stages.

In Brazil, weed management in sugarcane fields is mainly done with the use of selective herbicide formulations. For many years, diuron+hexazinone was one of the main herbicide mixture formulations used in sugarcane. Later, sulfometuron-methyl was included in the same mixture, which was marketed as a new herbicide formulation for residual in-season weed control in sugarcane. The mixture diuron+hexazinone+sulfometuron-methyl has been widely used in commercial sugarcane fields in Brazil. However, recent field observations have shown that sugarcane plants at different growth stages varied in their phytotoxicity levels after treatment with diuron+hexazinone+sulfometuron-methyl. Greenhouse and laboratory studies were conducted to determine 14Csulfometuron-methyl absorption and translocation, as well as 14C distribution in sugarcane at two growth stages, 2 to 3 leaves and 5 to 6 leaves. 14Csulfometuron-methyl absorption by sugarcane did not differ between the two growth stages. Different patterns of 14C accumulation were observed, which may explain variations in sulfometuron-methyl phytotoxic responses observed in the field.

Role of soil physicochemical properties in quantifying the fate of diuron, hexazinone, and metribuzin.

The physicochemical properties of soil are fundamental to quantification of the fate of herbicides. Thus, the aim of this research was to evaluate the fate of diuron, hexazinone, and metribuzin in five soils (Clay-1, Clay-2, Loam-1, Loam-2, and Sand), presenting variation in clay content, cation exchange capacity (CEC), pH, and organic carbon (OC). Herbicides radiolabeled with 14C were applied, and the 14C-CO2 released from mineralization was trapped in 0.2 mol L-1 sodium hydroxide solution. The degradation ratio, as well as herbicide-bound residues (non-extractable), transformation products, and residues extractable from soil, was also evaluated. Average 14C-CO2 evolution accumulated for diuron mineralization was higher (22.24%) than hexazinone (7.73%) and metribuzin (3.20%). The degradation time half-life (DT50) values for hexazinone correlated with soil OC content. Although no correlation between soil properties and DT50 values was found for metribuzin, the degradation rate and total degree of mineralization were low in sand soil for metribuzin. Regarding diuron, OC content and CEC value appear to be related to mineralization and degradation rate, respectively. Differences in soil properties can influence the persistence and fate of herbicides, affecting their impact on the environment, weed control, and possible effects on subsequent crops.

Leaching of Diuron, Hexazinone, and Sulfometuron-methyl Applied Alone and in Mixture in Soils with Contrasting Textures.

When herbicides are applied in mixture, interactions among them could potentially promote changes in herbicide behavior in the soil. Thus, application mode (isolated or in mixture) and soil texture (sandy or clayey) were investigated in the total leaching of the commercial mixture diuron + hexazinone + sulfometuron-methyl, and of each isolated compound. Experiments in soil columns also evaluated the movement of each herbicide and mixtures across soil layers. In the sandy soil, the greatest total leaching was observed with hexazinone compared to diuron and sulfometuron. Most of the applied diuron remained at the top layer of the soil, indicating that this herbicide has low soil mobility. Overall, our results show that hexazinone has greater leaching potential and mobility along the soil profile compared to diuron and sulfometuron. Our data can be used in assessing the fate of diuron, hexazinone, and sulfometuron alone or in mixture on natural ecosystems, under different soil types and application modes.

Uptake, translocation, and control of trumpet flower (Tecoma stans) with aminocyclopyrachlor.

To gain a better understanding of the physiology of the herbicide aminocyclopyrachlor in young plants of trumpet flower, the uptake and translocation were evaluated after the application of herbicide. This was determined by treating individual leaves with formulated herbicides plus (14)C-aminocyclopyrachlor after the application of the formulated herbicide. This experiment used a randomized experimental design with three replications. In addition, field studies were conducted to assess the effectiveness of foliar applications of aminocyclopyrachlor in association with metsulfuton-methyl. The plant absorbed 20% of the herbicide applied. The translocation percentage did not surpass 5% of the total amount applied. Only 1% of the herbicide applied was translocated to the roots. Rate of 40 + 13 g a.i. 100 L(-1) of aminocyclopyrachlor+metsulfuron-methyl was effective to control T. stans.

Chlorine dioxide against bacteria and yeasts from the alcoholic fermentation / Dióxido de cloro contra bactérias e leveduras da fermentação alcoólica

The ethanol production in Brazil is carried out by fed-batch or continuous process with cell recycle, in such way that bacterial contaminants are also recycled and may be troublesome due to the substrate competition. Addition of sulphuric acid when inoculum cells are washed can control the bacterial growth or alternatively biocides are used. This work aimed to verify the effect of chlorine dioxide, a well-known biocide for bacterial decontamination of water and equipments, against contaminant bacteria (Bacillus subtilis, Lactobacillus plantarum, Lactobacillus fermentum and Leuconostoc mesenteroides) from alcoholic fermentation, through the method of minimum inhibitory concentration (MIC), as well as its effect on the industrial yeast inoculum. Lower MIC was found for B. subtilis (10 ppm) and Leuconostoc mesenteroides (50 ppm) than for Lactobacillus fermentum (75 ppm) and Lactobacillus plantarum (125 ppm). Additionally, these concentrations of chlorine dioxide had similar effects on bacteria as 3 ppm of Kamoran® (recommended dosage for fermentation tanks), exception for B. subtilis, which could not be controlled at this Kamoran® dosage. The growth of industrial yeasts was affected when the concentration of chlorine dioxide was higher than 50 ppm, but the effect was slightly dependent on the type of yeast strain. Smooth yeast colonies (dispersed cells) seemed to be more sensitive than wrinkled yeast colonies (clustered cells/pseudohyphal growth), both isolated from an alcohol-producing unit during the 2006/2007 sugar cane harvest. The main advantage in the usage of chlorine dioxide that it can replace antibiotics, avoiding the selection of resistant populations of microorganisms.

A produção de etanol no Brasil é atualmente realizada pelo processo de fermentação em batelada alimentada ou contínuo, com reciclo de células de leveduras, de forma que contaminantes bacterianos são também reciclados e podem causar problemas devido à competição pelo mesmo substrato. O controle bacteriano é feito pela adição de ácido sulfúrico na lavagem das células do fermento ou utilizando-se biocidas. O objetivo do trabalho foi verificar o efeito do dióxido de cloro, um biocida muito utilizado para a descontaminação da água e equipamentos, contra bactérias contaminantes da fermentação alcoólica (Bacillus subtilis, Lactobacillus plantarum, Lactobacillus fermentum e Leuconostoc mesenteroides), através do método da concentração inibitória mínima (CIM), assim como seu efeito sobre o fermento industrial. Valores menores de CIM foram encontrados para Bacillus subtilis (10 ppm) e Leuconostoc mesenteroides (50 ppm) do que para Lactobacillus fermentum (75 ppm) e Lactobacillus plantarum (125 ppm). Estas concentrações tiveram o mesmo efeito inibidor que 3 ppm de Kamoran®, com exceção de B. subtilis, no qual não se observou inibição de crescimento à esta concentração. As leveduras industriais apresentaram inibição no crescimento em concentrações superiores a 50 ppm, porém esta pareceu ser dependente do tipo de linhagem de levedura. Colônias cremosas (células dispersas) foram ligeiramente mais sensíveis que as colônias rugosas (células agrupadas/pseudohifas), ambas isoladas de uma unidade produtora de álcool durante a safra de cana-de-açúcar 2006/2007. A principal vantagem na utilização deste produto está na eliminação do uso de antibióticos, evitando a geração de populações resistentes de microrganismos.

Chlorine dioxide against bacteria and yeasts from the alcoholic fermentation.

The ethanol production in Brazil is carried out by fed-batch or continuous process with cell recycle, in such way that bacterial contaminants are also recycled and may be troublesome due to the substrate competition. Addition of sulphuric acid when inoculum cells are washed can control the bacterial growth or alternatively biocides are used. This work aimed to verify the effect of chlorine dioxide, a well-known biocide for bacterial decontamination of water and equipments, against contaminant bacteria (Bacillus subtilis, Lactobacillus plantarum, Lactobacillus fermentum and Leuconostoc mesenteroides) from alcoholic fermentation, through the method of minimum inhibitory concentration (MIC), as well as its effect on the industrial yeast inoculum. Lower MIC was found for B. subtilis (10 ppm) and Leuconostoc mesenteroides (50 ppm) than for Lactobacillus fermentum (75 ppm) and Lactobacillus plantarum (125 ppm). Additionally, these concentrations of chlorine dioxide had similar effects on bacteria as 3 ppm of Kamoran® (recommended dosage for fermentation tanks), exception for B. subtilis, which could not be controlled at this Kamoran® dosage. The growth of industrial yeasts was affected when the concentration of chlorine dioxide was higher than 50 ppm, but the effect was slightly dependent on the type of yeast strain. Smooth yeast colonies (dispersed cells) seemed to be more sensitive than wrinkled yeast colonies (clustered cells/pseudohyphal growth), both isolated from an alcohol-producing unit during the 2006/2007 sugar cane harvest. The main advantage in the usage of chlorine dioxide that it can replace antibiotics, avoiding the selection of resistant populations of microorganisms.