(Beyond Pesticides, August 4, 2011) At least 21 different species of weeds are found to be resistant to the herbicide glyphosate, commonly sold as Roundup and used across thousands of acres of â€śRoundUp Readyâ€ť genetically engineered (GE) crops, according to a series of studies in the current issue of Weed Science.
Palmer amaranth, one of the weeds discussed in the journal, can reduce yields of cotton by more than 50 percent if there is a density of at least 10 of these weeds per row. Fifty-two counties in the state of Georgia had infestations of glyphosate-resistant Palmer amaranth last year. Studies confirm that the weed, which also competes with soybean, corn, grain sorghum and peanut crops, is also resistant to the herbicide phrithiobac in addition to glyphosate.
Over-application and over-reliance by farmers on glyphosate to solve all of their weed problems has led to the proliferation of so-called â€śsuper weeds,â€ť which have evolved to survive the treatments through repeated exposure. The most common species which have evolved these traits include pigweed (palmer amaranth), mareâ€™s tail, and ryegrass. The spread of resistance is what has led farmers to increasingly rely on more toxic alternative mixtures, including weed killers like atrazine. There has also been an increased push by chemical companies to engineer seed varieties that are resistant to multiple herbicide treatments, such as dicamba, glyphosate and 2,4-D, or glyphosate and acetochlor.
Contrary to common claims from chemical manufacturers and proponents of GE technology that the proliferation of herbicide tolerant GE crops would result in lower pesticide use rates, the data show that overall use of pesticides has remained relatively steady, while glyphosate use has skyrocketed to more than double the amount used just five years ago. The 2010 Agricultural Chemical Use Report shows that 57 million pounds of glyphosate were applied last year on corn fields in surveyed states. In the same states, ten years prior, in 2000, this number was only 4.4 million pounds, and in 2005, it was still less than half of current numbers at 23 million pounds.
The rise in glyphosate applications has almost certainly come as a result of farmers increasingly planting GE crops such as corn and soybeans, which are engineered to be resistant to the chemical. In this way, farmers can apply the chemical on a vast scale across their fields while not having to be careful that they donâ€™t hit their crops.
Glyphosate is a known carcinogen, neurotoxin, irritant, and has been found to kill human embryonic cells, and can cause kidney and liver damage. Glyphosate is also harmful to the environment, particularly aquatic life and water quality and has been linked to intersex frogs, and is lethal to amphibians in concentrations found in the environment.
As researchers scramble to find new ways of chemically coping with increased weed resistance, they overlook the glaring fact that there already exist alternative systems such as organic farming, which erases the need for these drastic measures through its systemic pest preventon approaches. Organic farming can be at least as productive as conventional, chemically-reliant farming while having none of the toxic side effects which create significant risks to ecosystems and human health. To learn more, see our page on organic food and agriculture.
Currently, there are commercially available glyphosate tolerant seed varieties for corn, soybeans, canola, sorghum, and cotton. Also, recently approved by the USDA were Roundup Ready versions of alfalfa and sugar beets. Due to serious questions regarding the integrity of USDAâ€™s environmental evaluations, public interest groups, including Beyond Pesticides, have filed suit against the agency to stop its full deregulation of GE alfalfa.