Marcus Barifouse Matallo

Agricultural impacts of glyphosate-resistant soybean cultivation in South America.

In the 2009/2010 growing season, Brazil was the second largest world soybean producer, followed by Argentina. Glyphosate-resistant soybeans (GRS) are being cultivated in most of the soybean area in South America. Overall, the GRS system is beneficial to the environment when compared to conventional soybean. GRS resulted in a significant shift toward no-tillage practices in Brazil and Argentina, but weed resistance may reduce this trend. Probably the highest agricultural risk in adopting GRS in Brazil and South America is related to weed resistance due to use of glyphosate. Weed species in GRS fields have shifted in Brazil to those that can more successfully withstand glyphosate or to those that avoid the time of its application. Five weed species, in order of importance, Conyza bonariensis (L.) Cronquist, Conyza canadensis (L.) Cronquist, Lolium multiflorum Lam., Digitaria insularis (L.) Mez ex Ekman, and Euphorbia heterophylla L., have evolved resistance to glyphosate in GRS in Brazil. Conyza spp. are the most difficult to control. A glyphosate-resistant biotype of Sorghum halepense L. has evolved in GRS in Argentina and one of D. insularis in Paraguay. The following actions are proposed to minimize weed resistance problem: (a) rotation of GRS with conventional soybeans in order to rotate herbicide modes of action; (b) avoidance of lower than recommended glyphosate rates; (c) keeping soil covered with a crop or legume at intercrop intervals; (d) keeping machinery free of weed seeds; and (d) use of a preplant nonselective herbicide plus residuals to eliminate early weed interference with the crop and to minimize escapes from later applications of glyphosate due to natural resistance of older weeds and/or incomplete glyphosate coverage.

Review of potential environmental impacts of transgenic glyphosate-resistant soybean in Brazil

Transgenic glyphosate-resistant soybeans (GRS) have been commercialized and grown extensively in the Western Hemisphere, including Brazil. Worldwide, several studies have shown that previous and potential effects of glyphosate on contamination of soil, water, and air are minimal, compared to those caused by the herbicides that they replace when GRS are adopted. In the USA and Argentina, the advent of glyphosate-resistant soybeans resulted in a significant shift to reduced- and no-tillage practices, thereby significantly reducing environmental degradation by agriculture. Similar shifts in tillage practiced with GRS might be expected in Brazil. Transgenes encoding glyphosate resistance in soybeans are highly unlikely to be a risk to wild plant species in Brazil. Soybean is almost completely self-pollinated and is a non-native species in Brazil, without wild relatives, making introgression of transgenes from GRS virtually impossible. Probably the highest agricultural risk in adopting GRS in Brazil is related to weed resistance. Weed species in GRS fields have shifted in Brazil to those that can more successfully withstand glyphosate or to those that avoid the time of its application. These include Chamaesyce hirta (erva-de-Santa-Luzia), Commelina benghalensis (trapoeraba), Spermacoce latifolia (erva-quente), Richardia brasiliensis (poaia-branca), and Ipomoea spp. (corda-de-viola). Four weed species, Conyza bonariensis, Conyza Canadensis (buva), Lolium multiflorum (azevem), and Euphorbia heterophylla (amendoim bravo), have evolved resistance to glyphosate in GRS in Brazil and have great potential to become problems.

INTERACTIONS OF SYNTHETIC HERBICIDES WITH PLANT DISEASE AND MICROBIAL HERBICIDES

Synthetic herbicides have the potential to influence plant disease by several mechanisms. They can enhance disease or protect plants from pathogens due to direct effects on the microbe, to effects on the plant, or to effects on both organisms. The particular effect is a function of many factors including the herbicide class and its formulation, the disease species, the plant species, timing of herbicide application and infection, and environmental factors. These secondary effects of herbicides have not been sufficiently studied to fully understand their environmental toxicology implications or their potential for enhanced integrated pest management. Furthermore, understanding these interactions can sometimes be critical in the success of biocontrol of weeds with plant pathogens.

Microwave-assisted solvent extraction and analysis of shikimic acid from plant tissues

A better method for determination of shikimate in plant tissues is needed to monitor exposure of plants to the herbicide glyphosate [N-(phosphonomethyl)glycine] and to screen the plant kingdom for high levels of this valuable phytochemical precursor to the pharmaceutical oseltamivir. A simple, rapid, and efficient method using microwave-assisted extraction (MWAE) with water as the extraction solvent was developed for the determination of shikimic acid in plant tissues. High performance liquid chromatography was used for the separation of shikimic acid, and chromatographic data were acquired using photodiode array detection. This MWAE technique was successful in recovering shikimic acid from a series of fortified plant tissues at more than 90% efficiency with an interference-free chromatogram. This allowed the use of lower amounts of reagents and organic solvents, reducing the use of toxic and/or hazardous chemicals, as compared to currently used methodologies. The method was used to determine the level of endogenous shikimic acid in several species of Brachiaria and sugarcane (Saccharum officinarum) and on B. decumbens and soybean (Glycine max) after treatment with glyphosate. The method was sensitive, rapid and reliable in all cases.

Sorption, Degradation, and Leaching of Tebuthiuron and Diuron in Soil Columns

Abstract A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.

Leaching and half-life of the herbicide tebuthiuron on a recharge area of Guarany aquifer in sugarcane fields in Brazil

This study was undertaken to evaluate the degradation and mobility of the herbicide tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) in soil under field conditions, and its potential for leaching and groundwater contamination. A watershed, Espraiado, located over a recharge area in Brazil, was chosen for soil and water studies. At Espraiado, water samples were collected from seven wells at intervals of three months from March 2004 to June 2006 and analyzed for tebuthiuron. Other samples were taken from city wells located outside of the recharge area. To assess the potential movement to the aquifer, tebuthiuron was also applied to trial plots at the recommended label rate of 1.0 kg/ha a.i. in May of 2004, with and without sugarcane coverage, on sandy soil. Soil samples were collected during the years of 2004 and 2005, at depths intervals of 20 cm from soil surface down to 120 cm and analyzed for tebuthiuron at zero, 3, 30, 60, 90, 120, 150, 180, 240, and 300 days after application. There was no clear effect of sugarcane coverage on the tebuthiuron degradation in soils, but it moved faster into the soil where there was no cover. After 180 days there were no measurable residues in the soil, and tebuthiuron was not found below 40 cm depth in any time. Tebuthiuron had a half-life of 20 days under those conditions. No tebuthiuron residue was found in ground water samples at any sampling time.

Adsorption of mecoprop and dichlorprop on calcareous and organic matter amended soils: Comparative adsorption of racemic and pure enantiomeric forms

Abstract The adsorption isotherms of mecoprop [R,S‐2‐(4‐chloro‐2‐ methylphenoxy) propanoic acid] and dichlorprop [R,S‐2‐(2,4‐dichlorophenoxy)propanoic acid] on twelve calcareous soils were studied. All the isotherms fit the Freundlich equation. The distribution coefficients (Kf) were low and were only significantly related with the organic matter content of the soils. The main adsorption mechanism at the pH of these soils was found to be by cation bridging between the anionic forms of the two herbicides, and the external surfaces of the organic matter and/or negatively charged clay. The Koc values for mecoprop (R,S‐ MCPP) and dichlorprop (R,S‐ DCPP) adsorption predicted a high mobility of these herbicides in the soils. Their corresponding enantiomeric forms, R (biologically active) and S (biologically inactive) were adsorbed at the same ratio on these soils. The organic matter amended soils showed a significant increase on the retention capacity of both molecules.

Movimento do herbicida tebutiuron em dois solos representativos das áreas de recarga do aqüífero Guarani

O movimento do herbicida tebutiuron foi analisado em um Latossolo Vermelho Distrofico psamitico (LVdq) e um Neossolo Quartzarenico Ortico tipico (RQo), representativos das areas de recarga do aquifero Guarani no Brasil, tendo como fatores influenciadores, a condutividade hidraulica (K), o teor de carbono orgânico (CO) e o teor de argila (TAr). O presente estudo foi realizado em colunas de solos indeformados, com aplicacao do produto comercial contendo o herbicida em discussao. Esses parâmetros evidenciam certa influencia na movimentacao vertical do herbicida tebutiuron, particularmente no RQo, uma vez que esse herbicida e quimicamente neutro. Observou-se, por exemplo, uma diferenca significativa entre os valores K dos dois solos, sendo superior no RQo. Alem de uma relacao inversa entre teores de CO e de TAr e os valores de K dos dois solos, indicando serem aqueles parâmetros inibidores do deslocamento do tebutiuron no perfil do solo. Os resultados aqui obtidos neste trabalho visam subsidiar estudos de avaliacao de risco ambiental, sobretudo agua subterrânea, a partir de areas de recarga de aquiferos naturalmente frageis, com enfase para o aquifero Guarani.

Glyphosate: influência na bioatividade do solo e ação de minhocas sobre sua dissipação em terra agrícola

The widespread usage of pesticides leads to the need of improving the knowledge on their environmental behaviour in order to decrease the risks to biota, as well as the water, soil, and food contamination. The influence of the earthworms Eisenia foetida on the dissipation of glyphosate, the herbicide bioaccumulation in the worms and the influence of the herbicide on the endogeneous microbial bioactivity were evaluated in an agricultural soil sample treated with aqueous solution of 14C-glyphosate. The studies were performed in systems maintained for 2 or 4 months containing soil samples treated with three different concentrations of 14C-glyphosate and containing or not the earthworms. After these periods, soil samples and the earthworms were extracted and combusted for radiocarbon quantification by liquid scintillation counting (ECL). The microbial bioactivity was evaluated through the activity of the dehydrogenase enzyme. Results showed that earthworms did not influence the soil dissipation of glyphosate, independently of the contact period, although they bioaccumulated glyphosate residues, proportionally to the contact period. The higher period favoured the 14C-non-extractable or bound residues production. Soil bioactivity was not altered, neither by the earthworms, nor by the treatments or time after treatments.

Sorption and desorption of Suflafenacil in two soils in the state of São Paulo with different physical and chemical attributes

A study was conducted to evaluate the sorption and desorption of 14C herbicide saflufenacil (pyrimidinedione) in two soils in the State of Sao Paulo, classified as Red Yellow Latosol with clayey texture (LVA-1) and medium texture (LVA-2), using the batch method through isotherms. The soils were air dried and sieved a 2 mm mesh. The radioactivity was determined by liquid scintillation spectrometry in acclimatized room (25 ± 2 °C). Sorption isotherms were conducted for 5 concentrations of saflufenacil (5.0; 2.5; 1.0; 0.5 and 0.05 μg mL-1) and the results were adjusted to the Freundlich equation, thus obtaining the parameters of sorption followed by two extractions with 0.01 M CaCl2 to determine desorption parameters similarly to sorption. The results showed that saflufenacil sorption was low for both soils studied, being greater for the LVA with higher organic matter content. The desorption coefficients were greater than their sorption coefficients, suggesting the occurrence of hysteresis. The sorption and desorption isotherms (classified as type C isotherms), hysteresis and the t-test between the angular coefficient of the respective isotherms showed that both the sorption and desorption occur with equal intensity.