Glyphosate Resistance in Weeds

The Institute of Science in Society 03/03/10

The Transgenic Treadmill

Glyphosate resistant weeds may spell the end of patented herbicide tolerant crops, but can farmers exit the transgenic treadmill that’s very profitable for Monsanto? Prof. Joe Cummins

Increasing instances of herbicide-resistant weeds are getting the attention of experts from around the world. IFT file photo

An evolving problem

Glyphosate herbicide was patented and sold by Monsanto corporation since 1974 under the trade name and proprietary formulation Roundup. The herbicide has been used widely in agriculture, forestry, aquaculture, alongside roads and highways, and in home gardening. Glyphosate is a broad-spectrum herbicide that poisons many plant species so it is frequently used to ‘burn down’ weeds on a field prior to the planting or emergence of crops.

Before 1996, weeds were not observed to have evolved resistance to glyphosate in the field, but since then, the introduction of transgenic glyphosate tolerant crops has led to evolution of a number of resistant weeds as the result of the greatly increased use of the herbicide particularly during the post-emergent growth of the crops. Glyphosate reisistant Asiatic dayflower (Commelina cumminus L) common lambsquarters (Chenopodium album L) and wild buckwheat (Polygonum convolvulus L) are reported to be increasing in prominence in some agro ecosystems as are populations of horseweed (Conyza canadensis (L) Cronq) [1].

In regions of the USA where transgenic glyphosate resistant crops dominate, there are now evolved glyphosate-resistant populations of the economically damaging weed species Ambrosia artemissifolia (rag weed), Ambrosia trifida L.(great ragweed), palmer pigweed (Amaranthus palmeri), common water hemp (Amaranthus rudis) , rough fruit amaranth (Amaranthus tuberculatus) and various Conyza (horse weed ) and Lolium (rye grass) species.

Likewise, in areas of transgenic glyphosate resistant crops in Argentina and Brazil, there are now evolved glyphosate  resistant populations of Johnson grass (Sorghum halepense) and Mexican fireplant (Euphorbia heterophylla) [2]. These herbicide resistant weeds pose a clear threat to the transgenic crops dominating North and South America [3].

More herbicide use reported on genetically modified crops

A report has found that farmers are using more herbicides on genetically engineered soybeans, corn, and cotton because of resistant weeds.

By Julie Masis Contributor to the Christian Science Monitor / December 21, 2009

A report released by the Organic Center found that the amount of herbicides used on genetically engineered crops has increased in the past 10 years, not decreased as might be expected. Since many genetically engineered crops were modified so that farmers could spray Roundup, or Glyphosate, to kill the weeds in their fields but not the crops themselves, the expectation was that less herbicide would be required. But the new report found that this is not what happened.

Wisconsin farmer Jim Lange loads a hopper of genetically modified corn. The blue color is insecticide covering kernels.

Biotech Crops Cause Big Jump In Pesticide Use: Report

Carey Gillam   Reuters   Nov 18, 2009

KANSAS CITY – The rapid adoption by U.S. farmers of genetically engineered corn, soybeans and cotton has promoted increased use of pesticides, an epidemic of herbicide-resistant weeds and more chemical residues in foods, according to a report issued Tuesday by health and environmental protection groups.

The groups said research showed that herbicide use grew by 383 million pounds from 1996 to 2008, with 46 percent of the total increase occurring in 2007 and 2008.

The report was released by nonprofits The Organic Center (TOC), the Union for Concerned Scientists (UCS) and the Center for Food Safety (CFS).

The groups said that while herbicide use has climbed, insecticide use has dropped because of biotech crops. They said adoption of genetically engineered corn and cotton that carry traits resistant to insects has led to a reduction in insecticide use by 64 million pounds since 1996.

Still, that leaves a net overall increase on U.S. farm fields of 318 million pounds of pesticides, which includes insecticides and herbicides, over the first 13 years of commercial use.