Glyphosate

Glyphosate, N-phosphonomethyl glycine, is broad-spectrum herbicide, sold under the brand name Roundup. It is "the most widely used broad-spectrum herbicide on [a] global scale." Some genetically engineered crops, sold as Roundup Ready Crops have their DNA altered to allow them to withstand glyphosate.

How It Works

Glyphosate is absorbed through a plant's foliage and then transported throughout the stems, leaves, and roots of the entire plant. A 2009 study says:

"The herbicidal effect is based on inhibition of the shikimate pathway enzyme 5-enolpyruvylshikimic acid-3-phosphate synthas (EPSPS), involved in the biosynthesis of aromatic amino acids and phenolic compounds."

A 1984 study found plants that died following treatment with glyphosate were infected with pathogenic fungi, compared to control plants not treated with glyphosate but planted in the same media that did not yield pathogenic fungi. The study concluded that more research was needed but postulated that glyphosate inhibits the plant's defense mechanisms and/or increases nutrient leakage from treated plants.

Impact on Non-Target Plants

Once glyphosate travels to a plant's roots, it is "released into the rhizosphere," (the area immediately around the roots), "where it is immobilized at the soil matrix or microbially degraded.

Impacts of Glyphosate Drift

At sub-lethal doses of glyphosate, such as the amounts a plant might be exposed to from spray drift, plants are still impacted. A study examined sunflowers treated with small amounts of glyphosate (to simulate spray drift) found:

"In conclusion, the results presented in this study showing that glyphosate is especially inhibitory to ferric reductase complement the recently published report (Eker etal., 2006) that glyphosate exerts a strong inhibitory influence on ferric reductase activity of Fe-deficient roots and impairs the uptake and translocation of Fe in plants. These impairments could be a major reason for the increasingly observed Fe deficiency chlorosis in cropping systems associated with widespread glyphosate usage as reported for different parts of the USA (Franzen etal., 2003; Jolley etal., 2004). Such strong interference of glyphosate with root uptake and root-to-shoot transport of Fe in crop plants may represent a potential threat to human and animal nutrition because of possible reduction of Fe in edible plants parts (e.g. seed/grain)."

In other words, low doses of glyphosate equal to the amount plants are exposed to in spray drift, can result in iron deficiencies in the plants. For crops destined as animal feed or as human food, this could result in decreased dietary iron.

Articles and resources

Related SourceWatch articles

• Monsanto
• Roundup Ready Crops
• Biotechnology

External resources

• Bott, S., Tesfamariam, T., Kania, A., Eman, B., Aslan, N., Roemheld, V., and Neumann, G. 2011, Phytotoxicity of glyphosate soil residues re-mobilised by phosphate fertilization. Plant Soil 315:2-11. DOI 10, 1007/s11104-010-06989-3.
• Schafer, J.R., Hallett, S.G., and Johnson, W.G. 2010. Role of soil-borne fungi in the response of giant ragweed (Ambrosia trifida) biotypes to glyphosate. Proc. Northcentral Weed Sci. Soc. 65:.
• Zobiole, L.H.S., Oliveira, R.S.Jr., Huber, D.M., Constantin, J., Castro, C., Oliveira, F.A., Oliveira, A. Jr. 2010. Glyphosate reduces shoot concentrations of mineral nutrients in glyphosate-resistant soybeans. Plant Soil 328:57-69.
• Zobiole, L.H.S., Oliveira, R.S. Jr., Kremer, R.J., Constantin, J., Yamada, T., Castro, C., Oliveiro, F.A., and Oliveira, A. Jr. 2010. Effect of glyposate on symbiotic N2 fixation and nickel concentration in glyphosate-resistant soybeans. Applied Soil Ecol. 44:176-180.
• Bellaloui, N., reddy, K.N., Zablotowicz, R.M., Abbas, H.K., and Abel, C.A. 2009. Effects of glyphosate application on seed iron and root ferric (III) reductase in soybean cultivars. J. Agric. Food Chem. 57:9569-9574.
• Cakmak, I., Yazici, A., Tutus, Y., Ozturk, L. 2009. Glyphosate reduced seed and leaf concentrations of calcium, magnesium, manganese, and iron in non-glyphosate resistant soybean. European J. Agron. 31:114-119.
• Kremer, R.J. and Means, N.E. 2009. Glyphosate and glyphosate-resistant crop interactions with rhizosphere microorganisms. European J. Agron. 31:153-161.
• Johal, G.R. and Huber, D.M. 2009. Glyphosate effects on diseases of plants. European J. Agron. 31:144-152.
• Fernandez, M.R., Zentner, R.P., Basnyat, P., Gehl, D., Selles, F., and Huber, D.M. 2009. Glyphosate associations with cereal diseases caused by Fusarium spp. in the Canadian Prairies. European J. Agon. 31:133-143.
• Yamada, T., Kremer, R.J., Camargo e Castro, P.R., and Wood, B.W. 2009. Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat to agricultural sustainability? European J. Agron. 31:111-113.
• Schafer, J.R., Westhoven, A.M., Kruger, G.R., Davis, V.M., Hallett, S.G., and Johnson, W.G. 2009. Effect of growth media on common lambsquarter and giant ragweed biotypes response to glyphosate. Proc. Northcentral Weed Sci. Soc. 64:102.
• Tsehaye Tesfamariam, S. Bott, I. Cakmak, V. Römheld, G. Neumann, "Glyphosate in the rhizosphere – role of waiting times and different glyphosate binding forms in soils for phytoxicity to non-target plants," European Journal of Agronomy (2009), 31:126-132.
• Levent Ozturk, Atilla Yazici, Selim Eker, Ozgur Gokmen, Volker Römheld, and Ismail Cakmak, "Glyphosate inhibition of ferric reductase activity in iron deficient sunflower roots," New Phytologist (2008), 177:899-906.
• Eker, S., Ozturk, L., Yazici, A., Erenoglu, B., Roemheld, V., and Cakmak, I. 2006. Foliar-applied glyphosate substantially reduced uptake and transport of iron and manganese in sunflower (Helianthus annuus L.) plants. J. Agric. Food Chem. 54:100019-10025.
• Larsen, R.L., Hill, A.L., Fenwick, A., Kniss, A.R., Hanson, L.E., and Miller, S.D. 2006. Influence of glyphosate on Rhizoctonia and Fusarium root rot in sugar beet. Pest Manag. Sci. 62:1182-1192.
• Johal, G.R. and Rahe, J.E. 1990. Role of phytoalexins in the suppression of resistance of Phaseolus vulgaris to Colletotrichum lindemuthianum by glyphosate. Canad. J. Plant Pathol. 12:225-235.
• Gurmukh S. Johal and James E. Rahe, "Effect of soilborne plant-pathogenic fungi on the herbicidal action of glyphosate on bean seedlings," Phytopathology (1984), 74:950-955.

External articles

• William Neuman and Andrew Pollack, "Farmers Cope With Roundup-Resistant Weeds," New York Times, May 3, 2010.

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