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ENVIRONMENTAL IMPACTS : SUPER WEEDSand Euphorbia heterophylla L. respectively. As transgenic glyphosate-resistantcrops will remain very popular with producers, it is anticipated that glyphosateresistantbiotypes of other prominent weed species will evolve over the next fewyears. Therefore, evolved glyphosate-resistant weeds are a major risk for thecontinued success of glyphosate and transgenic glyphosate-resistant crops.However, glyphosate-resistant weeds are not yet a problem in many parts of theworld, and lessons can be learnt and actions taken to achieve glyphosatesustainability. A major lesson is that maintenance of diversity in weed managementsystems is crucial for glyphosate to be sustainable. Glyphosate is essential forpresent and future world food production, and action to secure its sustainabilityfor future generations is a global imperative.http://onlinelibrary.wiley.com/doi/10.1002/ps.1525/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false12. Vila-Aiub M.M., Vidal A R, Balbi M.C, Gundel P.E, Trucco F, and Ghersa C.M.(2007) : Glyphosate-resistant weeds of South American cropping systems:an overview. Pest Management Science, 64, 366–371.Herbicide resistance is an evolutionary event resulting from intense herbicideselection over genetically diverse weed populations. In South America, orchard,cereal and legume cropping systems show a strong dependence on glyphosateto control weeds. The goal of this report is to review the current knowledge oncases of evolved glyphosate-resistant weeds in South American agriculture. Thefirst reports of glyphosate resistance include populations of highly diverse taxa(Lolium multiflorum Lam., Conyza bonariensis L., C. canadensis L.). In allinstances, resistance evolution followed intense glyphosate use in fruit fields ofChile and Brazil. In fruit orchards from Colombia, Parthenium hysterophorus L.has shown the ability to withstand high glyphosate rates. The recent appearance ofglyphosate-resistant Sorghum halepense L. and Euphorbia heterophylla L. inglyphosate-resistant soybean fields of Argentina and Brazil, respectively, is of majorconcern. The evolution of glyphosate resistance has clearly taken place in thoseagroecosystems where glyphosate exerts a strong and continuous selection pressureon weeds. The massive adoption of no-till practices together with the utilization ofglyphosate-resistant soybean crops are factors encouraging increase in glyphosateuse. This phenomenon has been more evident in Argentina and Brazil. The exclusivereliance on glyphosate as the main tool for weed management results inagroecosystems biologically more prone to glyphosate resistance evolution.13. Vidal A.R, Trezzi M.M, Prado R, Ruiz-Santaella J.P, and Vila-Aiub M. (2007):Glyphosate resistant biotypes of wild poinsettia (Euphorbia heterophyllaL.) and its risk analysis on glyphosate-tolerant soybeans. Journal of Food,Agriculture & Environment 5: 265–269.The continuous use of a single herbicide for weed control can result in selectionof biotypes resistant to that compound. Greenhouse experiments were conducted(119)