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Coupe et. al, 2012

Richard H Coupe, Stephen J Kalkhoff, Paul D Capelc, and Caroline Gregoired, “Fate and transport of glyphosate and aminomethylphosphonic acid in surface waters of agricultural basins,” Pest Management Science, 2012, 68:1, 16-30, DOI: 10.1002/ps.2212.

ABSTRACT:

BACKGROUND: Glyphosate [N-(phosphonomethyl)glycine] is a herbicide used widely throughout the world in the production of many crops and is heavily used on soybeans, corn and cotton. Glyphosate is used in almost all agricultural areas of the United States, and the agricultural use of glyphosate has increased from less than 10 000 Mg in 1992 to more than 80 000 Mg in 2007. The greatest intensity of glyphosate use is in the midwestern United States, where applications are predominantly to genetically modified corn and soybeans. In spite of the increase in usage across the United States, the characterization of the transport of glyphosate and its degradate aminomethylphosphonic acid (AMPA) on a watershed scale is lacking.

RESULTS: Glyphosate and AMPA were frequently detected in the surface waters of four agricultural basins. The frequency and magnitude of detections varied across basins, and the load, as a percentage of use, ranged from 0.009 to 0.86% and could be related to three general characteristics: source strength, rainfall runoff and flow route.

CONCLUSIONS: Glyphosate use in a watershed results in some occurrence in surface water; however, the watersheds most at risk for the offsite transport of glyphosate are those with high application rates, rainfall that results in overland runoff and a flow route that does not include transport through the soil. FULL TEXT

Zobiole et. al, 2010b

Luiz Henrique Saes Zobiole, Rubem Silvério de Oliveira Jr., Robert John Kremer, Jamil Constantin, Carlos Moacir Bonato, Antonio Saraiva Muniz, “Water use efficiency and photosynthesis of glyphosate-resistant soybean as affected by glyphosate,” Biochemistry and Physiology, 2010, 97: 182-193, DOI: 10.1016/j.pestbp.2010.01.004.

ABSTRACT:

Previous studies comparing cultivars of different maturity groups in different soils demonstrated that early maturity group cultivars were more sensitive to glyphosate injury than those of other maturity groups. In this work, we evaluated the effect of increasing rates of glyphosate on water absorption and photosynthetic parameters in early maturity group cultivar BRS 242 GR soybean. Plants were grown in a complete nutrient solution and subjected to a range of glyphosate rates either as a single or sequential leaf application. Net photosynthesis, transpiration rate, stomatal conductance, sub-stomatal CO2, carboxylation efficiency, fluorescence, maximal fluorescence and chlorophyll content were monitored right before and at different stages after herbicide application; water absorption was measured daily. All photosynthetic parameters were affected by glyphosate. Total water absorbed and biomass production by plants were also decreased as glyphosate rates increased, with the affect being more intense with a single full rate than half the rate applied in two sequential applications. Water use efficiency (WUE) was significantly reduced with increasing rates of glyphosate. FULL TEXT

Londo et al., 2014

Jason Paul Londo, John McKinney, Matthew Schwartz, Mike Bollman, Cynthia Sagers, and Lidia Watrud, “Sub-lethal glyphosate exposure alters flowering phenology and causes transient male-sterility in Brassica spp,” BMC Plant Biology, 2014, 14:70.

ABSTRACT:

BACKGROUND: Herbicide resistance in weedy plant populations can develop through different mechanisms such as gene flow of herbicide resistance transgenes from crop species into compatible weedy species or by natural evolution of herbicide resistance or tolerance following selection pressure. Results from our previous studies suggest that sub-lethal levels of the herbicide glyphosate can alter the pattern of gene flow between glyphosate resistant Canola®, Brassica napus, and glyphosate sensitive varieties of B. napus and B. rapa. The objectives of this study were to examine the phenological and developmental changes that occur in Brassica crop and weed species following sub-lethal doses of the herbicides glyphosate and glufosinate. We examined several vegetative and reproductive traits of potted plants under greenhouse conditions, treated with sub-lethal herbicide sprays.

RESULTS: Our results indicate that exposure of Brassica spp. to a sub-lethal dose of glyphosate results in altering flowering phenology and reproductive function. Flowering of all sensitive species was significantly delayed and reproductive function, specifically male fertility, was suppressed. Higher dosage levels typically contributed to an increase in the magnitude of phenotypic changes.

CONCLUSIONS: These results demonstrate that Brassica spp. plants that are exposed to sub-lethal doses of glyphosate could be subject to very different pollination patterns and an altered pattern of gene flow that would result from changes in the overlap of flowering phenology between species. Implications include the potential for increased glyphosate resistance evolution and spread in weedy communities exposed to sub-lethal glyphosate. FULL TEXT

Johnson et. al, 2009

William G. Johnson, Vince M. Davis, Greg R. Kruger, Stephen C. Weller, “Influence of glyphosate-resistant cropping systems on weed species shifts and glyphosate-resistant weed populations,” European Journal of Agonomy, 2009, 31, 162-172, DOI: 10.1016/j.eja.2009.03.008.

ABSTRACT:

Glyphosate-resistant (GR) crops have facilitated increases in conservation tillage production practices and simplified weed control in GR corn, soybean, canola and cotton. Increased reliance on glyphosate, many times as the only active ingredient used, has resulted in weed species shifts and the evolution of weed populations resistant to glyphosate. However, weed shifts and the evolution of herbicide resistance are not new in regard to glyphosate use. Similar effects have been documented to many other historically important weed control advancements for agricultural crop production. GR crop technology was developed to utilize glyphosate for postemergence weed control and industry scientists suggested that there was little fear of weed shifts and resistance evolution due to the broad spectrum of weeds controlled by glyphosate. However, over the last decade, the most problematic weeds in agronomic cropping systems have shifted away from perennial grass and perennial broadleaf weeds to primarily annual broadleaf weeds. The evolution of several GR annual broadleaf weeds in GR cropping systems has been documented, and glyphosate resistance mechanisms in weeds are currently poorly understood. FULL TEXT

Bonini et al., 2009

E.A. Bonini, M.L.L. Ferrarese, R. Marchiosi, P.C. Zonetti, O. Ferrarese-Filho, “A simple chromatographic assay to discriminate between glyphosate-resistant and susceptible soybean (Glycine max) cultivars,” European Journal of Agronomy, 2009, 31:3, 1730176, DOI: 10.1016/e.eja.2009.03.006.

ABSTRACT:

In glyphosate-susceptible soybean (Glycine max L. Merrill), the herbicide glyphosate [(N-phosphonomethyl)glycine] inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, causing a massive accumulation of the metabolite shikimate. This phenomenon does not occur in glyphosate-resistant soybean due the presence of a gene encoding glyphosate-insensitive EPSP synthase. This study proposes a simple and reliable assay as an alternative tool for differentiating glyphosate-resistant from susceptible soybean cultivars. The assay is based on a single extraction of leaf or root tissue. Shikimate is quantified by reversed-phase high–performance liquid chromatography at 220 nm and isocratic elution with phosphoric acid. After glyphosate treatment, tissues of glyphosate-susceptible plants were found to massively accumulate shikimate, whereas the tissues of glyphosate-resistant plants did not accumulate the metabolite. FULL TEXT

Yamada, 2009

T. Yamada, “Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat to agricultural sustainability?,” European Journal of Agronomy, 2009, 31:3, 111-176.

ABSTRACT:

Not Available

FULL TEXT

Cakmak et. al, 2009

Ismail Cakmak, Atilla Yazici, Yusuf Tutus, Levent Ozturk, “Glyphosate reduced seed and leaf concentrations of calcium, manganese, magnesium, and iron in non-glyphosate resistant soybean,” European Journal of Agronomy, 2009, 31:3, 114-119, DOI: 10.1016/e.eja.2009.07.001.

ABSTRACT:

Greenhouse experiments were conducted to study the effects of glyphosate drift on plant growth and concentrations of mineral nutrients in leaves and seeds of non-glyphosate resistant soybean plants (Glycine max, L.). Glyphosate was sprayed on plant shoots at increasing rates between 0.06 and 1.2% of the recommended application rate for weed control. In an experiment with 3-week-old plants, increasing application of glyphosate on shoots significantly reduced chlorophyll concentration of the young leaves and shoots dry weight, particularly the young parts of plants. Concentration of shikimate due to increasing glyphosate rates was nearly 2-fold for older leaves and 16-fold for younger leaves compared to the control plants without glyphosate spray. Among the mineral nutrients analyzed, the leaf concentrations of potassium (K), phosphorus (P), copper (Cu) and zinc (Zn) were not affected, or even increased significantly in case of P and Cu in young leaves by glyphosate, while the concentrations of calcium (Ca), manganese (Mn) and magnesium (Mg) were reduced, particularly in young leaves. In the case of Fe, leaf concentrations showed a tendency to be reduced by glyphosate. In the second experiment harvested at the grain maturation, glyphosate application did not reduce the seed concentrations of nitrogen (N), K, P, Zn and Cu. Even, at the highest application rate of glyphosate, seed concentrations of N, K, Zn and Cu were increased by glyphosate. By contrast, the seed concentrations of Ca, Mg, Fe and Mn were significantly reduced by glyphosate. These results suggested that glyphosate may interfere with uptake and retranslocation of Ca, Mg, Fe and Mn, most probably by binding and thus immobilizing them. The decreases in seed concentration of Fe, Mn, Ca and Mg by glyphosate are very specific, and may affect seed quality. FULL TEXT

Fernandez et. al, 2009

M.R. Fernandez, R.P. Zentner, P. Basnyat, D. Gehl, F. Selles, D. Huber, “Glyphosate associations with cereal diseases caused by Fusarium spp. in the Canadian Prairies,” Eurpoean Journal of Agronomy, 2009, 31:3, 133-143, DOI: 10.1016/j.eja.2009.07.003.

ABSTRACT:

Fusarium pathogens cause important diseases, such as root/crown rot and Fusarium head blight (FHB), in cereal crops. These diseases can be caused by similar Fusarium spp. Common root rot (CRR) is widespread in the western Canadian Prairies, whereas FHB has potential of becoming an important disease in this region. There are no commercially available cereal cultivars with good resistance to these diseases. It is therefore important to identify agronomic practices that could affect levels of Fusarium pathogens in cereals. This review deals primarily with the effects of tillage systems and glyphosate use on the development of FHB and CRR in wheat and barley in eastern Saskatchewan. Although the FHB study in 1999–2002 indicated that environment was the most important factor determining FHB development, previous glyphosate use and tillage practice were among the production factors with the greatest association with FHB. Overall, disease was highest in crops under minimum-till management. Previous glyphosate use was consistently associated with higher FHB levels caused by the most important FHB pathogens, Fusarium avenaceum and Fusarium graminearum. Cochliobolus sativus, the most common CRR pathogen, was negatively associated with previous glyphosate use, while F. avenaceum, F. graminearum, and other fungi were positively associated, suggesting that glyphosate might cause changes in fungal communities. The occurrence and isolation of F. avenaceum from cereal residues were greater under reduced-till than conventional-till while C. sativuswas most common under conventional-till, and F. graminearum was lowest under zero-till. Previous glyphosate applications were again correlated positively with F. avenaceum and negatively with C. sativus. These observations agreed with results from the FHB and CRR studies. These are the first studies that established a relationship between previous glyphosate use and increased Fusarium infection of spikes and subcrown internodes of wheat and barley, or Fusarium colonization of crop residues. However, because of the close association between noncereal crops, reduced tillage and glyphosate use, it was not possible to completely separate the effects of these factors on Fusarium infections. Determining the relative contribution of these popular production trends to the development of diseases caused by Fusarium spp. are essential for devising appropriate agronomic recommendations to prevent their further spread in western Canada, and to reduce the impact that these diseases are having in areas where they are already established. The consistent association between previous glyphosate use and Fusarium infections also warrants further research to elucidate the nature of this association and the underlying mechanisms determining these effects. FULL TEXT

Oliveira et. al, 2016

Regis de Campos Oliveira, Lucas Kortz Vilas Boas, and Ciro Cesar Zanini Branco, “Assessment of the potential toxicity of glyphosate-based herbicides on the photosynthesis of Nitella microcarpa var. wrightii (Charophyceae),” Phycologia, 2016, 55:5, 577-584, DOI: 10.2216/16-12.1.

ABSTRACT:

Although macroalgae are considered one of the most important primary producers in streams, to our knowledge there has been no research on the effects of herbicides on these organisms. Such studies are crucial for improving our understanding of the impact of these substances on stream ecology. In this study, we assess the effects of technical-grade glyphosate, Roundup and aminomethylphosphonic acid (AMPA; the main degradation product of glyphosate) on the photosynthetic rate, dark respiration rate and chlorophyll a content of Nitella microcarpa var. wrightii, a green algae found worldwide. Three concentrations of technical-grade glyphosate and Roundup were tested (0.28, 3.5 and 6 mg l1), while for AMPA only one concentration was evaluated (0.03 mg l1). Our results indicate that glyphosate has a stronger inhibitory effect on photosynthetic rate when applied in association with a surfactant (Roundup). These effects are related both to the concentration of the active ingredient and to exposure time. On the other hand, treatment with AMPA had a stimulatory effect on the photosynthetic rate, which may be associated with an increased supply of phosphorus available to the algae from the AMPA degradation process. From an ecological perspective, our results show that the ecological distribution of N. microcarpa var. wrightii, in terms of both spatial and temporal scales, can be affected by glyphosate-based herbicides in streams. FULL TEXT

Cuhra et. al, 2014

M. Cuhra, T. Traavik, and T. Bohn, “Life cycle fitness differences in Daphnia magna fed Roundup-Ready soybean or convetional soybean or organic soybean,” Aquaculture Nutrition, 2014, DOI: 10.1111/ani.12199.

ABSTRACT:

A lifelong feeding study with soybean from different production systems was carried out in the crustacean Daphnia magna (water flea), an acknowledged model organism for ecotoxicological studies. Experimental diets were prepared with soybean meal from different agriculture production systems: (i) genetically modified Roundup-Ready soy (Glyphosate-Tolerant), (ii) conventional soy and (iii) soy from organic agriculture (agriculture with neither synthetic pesticides nor synthetic fertilizers). Overall, feed produced from organic soybeans resulted in the highest fitness (higher survival, better growth and fecundity) in the model organism. Animals fed Roundup-Ready soybean consistently performed less well compared to animals fed either conventional or organic soybeans. We conclude that accumulation of herbicide residues in Roundup-Ready soy and related nutritional differences between the soy types may have caused the observed fitness differences. The results accentuate the need for further research clarifying qualitative aspects, including potential large-scale consequences for food and feed quality, of this dominant crop. FULL TEXT

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