A study from the United States has revealed that the increase in proliferation of herbicide-resistant weeds has led farmers in the country to dramatically increase the amount of herbicides used on their crops. Furthermore, the study’s chief author said the use of older, more damaging chemicals is becoming more widespread as a result of the change.

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Professor Charles Benbrook, of the Center for Sustaining Agriculture and Natural Resources at Washington State University, found herbicide use in the production of three genetically modified herbicide-tolerant crops (cotton, soybeans and corn) has increased, in contrast to industry claims that the pants would lead to a reduction in the use of damaging chemicals.

Benbrook said his “counterintuitive finding is based on an exhaustive analysis of publicly available data from the U.S. Department of Agriculture’s National Agriculture Statistics Service.” He looked at data for GM crops which have been grown commercially in the US since 1996. Over the period, pesticide use was shown to have increased by a total of 183 million Kilograms.

The peer reviewed study echoes the findings of research conducted by the Pesticide Action Network and other sustainable farming organisations in the United States; a recent study conducted by the US-based Organic Center showed GM crops were treated with 26 per cent more chemicals than conventional varieties in 2008.

Dr Marcia Ishii-Eiteman, a senior scientist at Pesticide Action Network, commented on the situation that has arisen in the US, "Rather than reducing the need for hazardous pesticides, herbicide-resistant seeds have driven a massive increase in herbicide use that has been linked to significant environmental and public health concerns. It's clear that genetically engineered, herbicide-resistant seeds are the growth engines of the pesticide industry's sales and marketing strategy. These seeds are part of a technology package explicitly designed to facilitate increased, indiscriminate herbicide use and pump up chemical sales."

Superweeds

Whereas Dr Ishii-Eiteman blames an agricultural paradigm that is unsustainable and narrow in focus, and advocates a more holistic approach to farming, professor Benbrook puts down the increased chemical use to the emergence and spread of glyphosate-resistant weeds, which, although their existence was initially denied by chemical manufacturers, are now present in 13 US States. Benbrook’s research shows the resistant crops’ emergence is strongly correlated with the upward trajectory in herbicide use.

In the United States, 95 percent of soybean and cotton acres, and over 85 percent of corn, are planted to varieties genetically modified to be herbicide resistant. However, although seed companies recommend farmers rotate crops and adopt other measures to avoid the development of glyphosate resistance in field weeds, high market prices for these staples have seen many farmers ignore this advice. Whilst chemical manufacturers blame greedy farmers for the superweeds, sustainable agriculture experts have said resistance is an inevitability, and that this practice has only exacerbated a latent problem with current industrial techniques.  

The professor commented, “Resistant weeds have become a major problem for many farmers reliant on [GM] crops, and are now driving up the volume of herbicide needed each year by about 25 percent,”

His study shows a marked annual increase in the herbicides required to deal with ‘superweeds,’ control of which is becoming ever more difficult. Many farmers in the US have expressed fears that they will have to return to traditional weeding methods, which would be nigh on impossible in the vast fields which the advent of GM technology has enabled them to plant. The annual increase in herbicide use on GM cultivars has grown from around 680,000 Kg in 1999 to about 41 million Kg in 2011 in the US.

Benbrook stated that, although herbicide-tolerant crops worked extremely well in the first few years of use, “over-reliance may have led to shifts in weed communities and the spread of resistant weeds that force farmers to increase herbicide application rates (especially glyphosate), spray more often, and add new herbicides that work through an alternate mode of action into their spray programs.”

Discussing the implications of this shift, Benbrook said, “Things are getting worse fast; In order to deal with rapidly spreading resistant weeds, farmers are being forced to expand use of older, higher-risk herbicides [and] spray the insecticides that [pest-resistant] Bt corn and cotton were designed to displace."

In Europe, only one GM crop is licensed for commercial cultivation. Monsanto’s MON810 maize, licensed to be grown for use in animal feed and sold as Yieldgard, is planted in a number of countries, though eight EU states have banned production of the grain.   

A detailed summary of the study, Impacts of genetically engineered crops on pesticide use in the U.S. — the first sixteen years, is available here. The study itself is available here.

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