Glyphosate Resistant Weeds (Hansard, 30 January 2003)

§ The Parliamentary Under-Secretary of State, Department for Environment, Food and Rural Affairs (Lord Whitty)

The Government are aware of the emergence of glyphosate resistant weeds resulting from the continuous use of this herbicide on some genetically modified herbicide tolerant (GMht) soya crops in Amercia. Over the past 30 years or more (before the advent of GM crop cultivation), continual use of herbicides has imposed selection pressure for increased resistance within weed species that were formally susceptible. There are several characteristics of herbicides and their use that are thought to contribute to a high risk for selection of resistance in weeds. Glyphosate meets these criteria and is one of the herbicides to which resistant weeds have evolved.

An international survey of herbicide resistant weeds identified Horseweed (Conyza Canadensis) as the main glyphosate resistant weed in America (in Delaware, Tennessee, Indiana, Maryland, New Jersey and Ohio). The only other glyphosate resistance species identified in this survey was in California—rigid ryegrass (Lolium rigidum—please refer to http://www.weedscience.org/in.asp). As Horseweed and rye grass are not sexually compatible with soya (Glycine max), glyphosate resistance was not acquired through the transfer of genes from the herbicide resistant soya.

Part of the UK's pesticide regulatory regime requires pesticide approval holders to address the risk of resistance and, if applicable, produce a management strategy to avoid or manage resistance. This applies equally to GMht and conventional crops alike. In addition, under the GMO safety legislation (Directive 2001/18/EU), management strategies applied to GM crops are considered as part of a detailed risk assessment.