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 C were applied, and theC-CO released from mineralization was trapped in 0.2 mol L 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 C-CO 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.

This study aimed to evaluate the sorption-desorption and leaching of aminocyclopyrachlor from three Brazilian soils. The sorption-desorption of C-aminocyclopyrachlor was evaluated using the batch method and leaching was assessed in glass columns. The Freundlich model showed an adequate fit for the sorption-desorption of aminocyclopyrachlor. The Freundlich sorption coefficient [K] ranged from 0.37 to 1.34 µmol L kg and showed a significant positive correlation with the clay content of the soil, while the K ranged from 3.62 to 5.36 µmol L kg. The K values were higher than their respective K, indicating that aminocyclopyrachlor sorption is reversible, and the fate of this herbicide in the environment can be affected by leaching. Aminocyclopyrachlor was detected at all depths (0-30 cm) in all the studied soils, where leaching was influenced by soil texture. The total herbicide leaching from the sandy clay and clay soils was <0.06%, whereas, ∼3% leached from the loamy sand soil. The results suggest that aminocyclopyrachlor has a high potential of leaching, based on its low sorption and high desorption capacities. Therefore, this herbicide can easily contaminate underground water resources.

-Tolerance, also referred to as natural resistance, is a feature that exists in the plant even before herbicide application in an area. I. grandifolia, I. indivisa and I. purpurea are among the tolerant species most commonly found over fields in southern Brazil. We hypothesized that the intensive use of glyphosate results in increasing levels of tolerance to glyphosate, and in pronounced response variability in populations of the same Ipomoea species. This study aimed at identifying tolerance variations to glyphosate among I. grandifolia, I. indivisa and I. purpurea morning glory species and among populations of these species. In crops over Paraná and Santa Catarina states (Brazil) 31 biotypes were collected (20 I. grandifolia, 7 I. indivisa and 4 I. purpurea), on which were applied 0, 216, 432, 864, 1,296, 1,728 and 2,160 g a.e. ha -1 of glyphosate and the dose required to reduce 50% of dry matter (GR 50 ) was determined. Biotypes of all tested Ipomoea species showed variability of glyphosate tolerance. Tolerance factors had greater amplitude among biotypes of I. gradifolia and I. indivisa species (between 1.7 and 33.6 and between 3.3 and 34.2, respectively) than in I. purpurea (between 3.7 and 4.9). Especially within I. gradifolia e I. indivisa species, some biotypes required a much higher dose than the recommended one to control the wild biotype, indicating progress in the level of glyphosate tolerance; this proves the initial hypothesis of this work. Keywords

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O Paspalum virgatum L. é uma planta daninha comum de pastagens e possui difícil controle, principalmente devido sua semelhança com as forrageiras. As técnicas convencionais como gradagem e replantio da pastagem têm sido insatisfatórias no controle desta planta daninha. O objetivo deste trabalho foi avaliar o controle do capim-navalha (P. virgatum L.) à atrazine aplicada em pré-emergência, por meio de curva dose-resposta e a seletividade deste herbicida nas pastagens de Brachiaria brizantha cv. Marandu e Panicum maximum cv. Mombaça. Foram realizados três experimentos independentes, com cada espécie, em dois tipos de solo (Latossolo Vermelho Amarelo distrófico - LVAd de textura franco-argilosa e Argissolo Vermelho Amarelo distrófico - PVAd de textura franca), utilizando a escala percentual de notas para verificar o controle do capim-navalha e a fitotoxicidade nas forrageiras e massa seca no final dos experimentos. A atrazine controlou o capim-navalha, desde os 15 dias após a aplicação (DAA), nas doses abaixo da recomendação do fabricante (250 e 500 g ha-1 i.a.). Contudo, apesar dos sintomas de fitotoxicidade causados pela atrazine, houve retomada de crescimento aos 60 DAA tanto para B. brizantha cv. Marandu quanto para P. maximum cv. Mombaça. Houve menor fitotoxicidade às pastagens no solo de textura franco‑argilosa em relação ao solo de textura franca. A atrazine proporcionou controle eficiente do P. virgatum L. (500 g ha-1 i.a.) quando aplicada em pré-emergência e seletividade para B. brizantha cv. Marandu (<2.000 g ha-1 i.a.) e P. maximum cv. Mombaça (<500 g ha-1 i.a.).

Glyphosate is easily exuded by the roots of plants. However, there is still some lack of information in the scientific literature as to whether Urochloa brizantha is capable of exuding glyphosate to influence the growth of crops such as sugarcane and citrus. Thus, the objective of this research was to evaluate the translocation and root exudation of 14 C-glyphosate by U. brizantha and its transport in sugarcane and citrus. Sugarcane seedlings, varieties SP80-1842, and citrus 'Limão Rosa' (Citrus limonia L. Osbeck) were cultivated with U. brizantha around the seedlings. Using a microsphere, 14 C-glyphosate was applied on the leaves of U. brizantha. The plants were cultured for 12 days after treatment (DAT). The radioactivity of the herbicide was evaluated by liquid scintillation spectrometer, after oxidizing the soil and parts of the plants (leaves, culms and roots) of U. brizantha, sugarcane and citrus. The highest amount of glyphosate was detected in the U. brizantha leaves, where the applications were carried out, regardless of the culture studied. Only traces of glyphosate (0.001%) were detected in soil cultivated with sugarcane. On the other hand, in citrus, U. brizantha exuded 9.46% of the glyphosate by the root system in the soil. The total amount of herbicide found in sugarcane and citrus seedlings was only 0.006 and 0.095%, respectively, in all parts of the plant. These concentrations are lower than those required to cause intoxication in those crops. Considering the results, it is possible to state that the translocation of glyphosate in young plants of U. brizantha associated with citrus was higher in relation to sugarcane, and it was not exuded by the root system of the weed with sugarcane, but presented root exudation with citrus, however, the amount did not reach what is necessary to affect the dry mass of the agricultural crops.Keywords: behavior in the plant, radioisotope, chemical sensitivity. RESUMO-O glyphosate é facilmente exsudado pelas raízes das plantas. No entanto, ainda falta informação na literatura científica sobre a braquiária (Urochloa brizantha) é capaz de exsudar o glyphosate a ponto de influenciar o crescimento de culturas, como cana-de-açúcar e citros. Assim, o objetivo desta pesquisa foi avaliar a translocação e exsudação radicular do 14 C-glyphosate por U. brizantha e seu transporte em mudas de cana-de-açúcar e citros. Foram cultivadas mudas de cana-de-açúcar, variedade SP80-1842, e citros 'Limão Rosa' (Citrus limonia L. Osbeck) com a braquiária ao redor das mudas. Utilizando uma microsseringa, foi aplicado 14 C-glyphosate nas folhas de braquiária. As plantas foram cultivadas por 12 dias após o tratamento (DAT). A radioatividade do herbicida foi avaliada por espectrômetro de cintilação líquida, depois de oxidado o solo e as partes das Planta Daninha 2019; v37:e019183334 VITI, M.L. et al. Translocation and root exudation of glyphosate by Urochloa brizantha and its transport on sugarcane ...2 plantas (folhas, colmos e raízes) de braquiária, cana-de-açúcar e citros. A maior quantida...

Abstract:Aminocyclopyrachlor is an herbicide that belongs to the new class of chemicals known as the pyrimidine carboxylic acids, which are used to control broadleaf weeds and brush. However, the environmental behavior and fate of aminocyclopyrachlor are not fully understood. The aim of the present study was thus to evaluate the mineralization, extractable residue and bound residue formation of aminocyclopyrachlor in three tropical soils with different physico-chemical properties. 14 C-labeled [pyrimidine-2-14 C] aminocyclopyrachlor was used to assess the fate of this herbicide in soil placed in biometer culture flasks. Total mineralization (accumulated 14 CO 2 ) of aminocyclopyrachlor was found to be <10% in all soils, decreasing in the following order: Oxisol-Typic Hapludox (clay) > Oxisol-Typic Hapludox (loamy sand) > Plinthosol-Petric (sandy clay). Overall, constant rate of mineralization (k) values for all soils were very low (0.00050% to 0.00079% 14 CO 2 day −1 ), with mineralization half-life times (MT50) consequently very high (877 to 1376 days), suggesting potential long persistence in soil. The amount of extractable residues decreased from~31% to 50% in all soils after 126 days of incubation, indicating an increase in bound residue formation from~5.0-to 7.5-fold compared to evaluation immediately after herbicide application, suggesting that degradation herbicide is involved in the formation of bound residues. Extractable residues are important factors that control mineralization and bound residue formation from aminocyclopyrachlor in the soil. The present study is the first to assess the fate, distribution, and formation of bound residues of aminocyclopyrachlor in soils. Aminocyclopyrachlor residues were predominantly associated with the OM and clay contents of soil. This effect of soil physico-chemical properties should be considered in environmental risk assessment of aminocyclopyrachlor and its application in the field for weed control.

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