5.2 Myth: GM crops decrease pesticide use

Truth: GM crops increase pesticide use

GM crops are claimed by proponents to reduce pesticide use (the term “pesticide” includes herbicides, which technically are pesticides). But this is untrue. Herbicide-tolerant crops have been developed specifically to depend upon agrochemicals and have extended the market for these chemicals. Far from weaning agriculture away from environmentally damaging chemicals, GM technology has prolonged and extended the chemically-based agricultural model.

The increased adoption of GM Roundup Ready crops, especially soy, has been accompanied by massive increases in the use of glyphosate herbicides worldwide.^1,2,3,4,5,6

North America

A report by agronomist Dr Charles Benbrook based on US Department of Agriculture data looked at the effects on pesticide use of the first sixteen years of GM crop cultivation in the United States, from 1996 to 2011. Benbrook analyzed the impact of the six major GM pest-management traits on pesticide use. The crops taken into account were herbicide-tolerant maize, soybeans, and cotton; Bt maize targeting the European corn borer and corn rootworm; and Bt cotton targeting Lepidopteran insects (butterflies and moths).²

The report found that GM herbicide-tolerant crops have led to a 239 million kilogram (527 million pound) increase in herbicide use in the United States between 1996 and 2011, while Bt crops have reduced chemical insecticide spray use by 56 million kilograms (123 million pounds). Overall pesticide use increased by an estimated 183 million kg (404 million pounds), or about 7%, compared with the amount that would have been used if the same acres had been planted to non-GM crops.²

Herbicide-tolerant soybeans accounted for 70% of the total increase across the three herbicide-tolerant crops. Rising reliance on glyphosate accounted for most of this increase.²

Moreover, GM herbicide-tolerant soy is increasing the use of herbicides over time, whereas non-GM soy is decreasing herbicide use, clearly showing that GM soy is not sustainable. In 1996 GM herbicide-tolerant soy needed 0.30 pounds per acre less herbicide than non-GM soy. But in 2011 the cultivation of GM herbicide-tolerant soy needed 0.73 pounds per acre more herbicide than non-GM soy.²

This data is unsurprising, since the pesticide industry is the GM seed industry.⁷ It is in its interest to produce seeds that are dependent on pesticides.

Two major factors are driving the upward trend in herbicide use on herbicide-tolerant acres compared to acres planted to non-GM crops: incremental reductions in the application rate of herbicides other than glyphosate applied to non-GM crops and the rapid spread of glyphosate-resistant weeds. The first factor is driven by the pesticide industry trend of selling more potent herbicides effective at lower rates of application.

The area of US cropland infested with glyphosate-resistant weeds expanded to 61.2 million acres in 2012, according to a survey conducted by Stratus Agri-Marketing. Nearly half of all US farmers interviewed reported that glyphosate-resistant weeds were present on their farm in 2012, up from 34% of farmers in 2011. The survey also indicates that the rate at which glyphosate-resistant weeds are spreading is gaining momentum; increasing 25% in 2011 and 51% in 2012.^8,9

South America

The same trend of increasing herbicide use has been found in South America since the introduction of GM herbicide-tolerant soy. In Argentina, as the area planted to GM herbicide-tolerant soy increased from 0.4 million hectares in 1996/97 to 14.1 million hectares in 2003/04, the volume of glyphosate applied to soybeans increased from 0.82 million kg in 1996/97 to 45.86 million kg in 2003/04. Between 1999 and 2003 the volume of glyphosate applied to soy increased by 145% (figures are from the Argentine crop protection industry association, CASAFE, as no official government data are available).³

These increases in herbicide use are to be expected, given the expansion in area planted to GM herbicide-tolerant soy in that period. However, as in North America, each year, farmers have had to apply more glyphosate per hectare than the previous year to achieve weed control. The average rate of glyphosate application on soy increased steadily from 1.14 kg/hectare in 1996/97 to 1.30 kg/hectare in 2003/04.³
Increasing rates of herbicide use per hectare over time has also been found in Brazil. In the state of Rio Grande do Sul, where GM soy was first planted illegally in 1998, use of glyphosate increased 85% between 2000 and 2005, while the area of soy cultivation increased by only 30.8%, according to the Brazilian Institute of the Environment (IBAMA).¹⁰

Glyphosate-resistant superweeds

The widespread use of Roundup Ready crops has led to over-reliance on a single herbicide – glyphosate, commonly sold as Roundup. This has resulted in the rapid spread of glyphosate-resistant weeds in regions where GM crops are planted.^1,11 Resistant weeds include pigweed,¹² ryegrass,¹³ and marestail.¹⁴

The International Survey of Herbicide Resistant Weeds’ website lists 28 glyphosate-resistant weeds around the world.¹⁵

When resistant weeds first appear, farmers often use more glyphosate herbicide to try to control them. But as time passes, no amount of glyphosate herbicide is effective.¹¹¹² Farmers are forced to resort to potentially even more toxic herbicides and mixtures of herbicides, including 2,4-D (an ingredient of the Vietnam defoliant Agent Orange) and dicamba.^{1,13,14,16,17,18,19,20}

Some US farmers are going back to more labour-intensive methods like ploughing – and even pulling weeds by hand.²¹ In Georgia in 2007, 10,000 acres of farmland were abandoned after being overrun by glyphosate-resistant pigweed.²² One report said the resistant pigweed in the Southern US was so tough that it broke farm machinery.²³

Another report said of the Roundup Ready system, “This silver bullet of American agriculture is beginning to miss its mark.”²⁴ As glyphosate-resistant weeds undermine the Roundup Ready farming model, Monsanto has taken the extraordinary step of paying farmers to spray other herbicides to supplement Roundup.^20,21

How are superweeds created?

Many glyphosate-resistant weeds appear through what is known as selection pressure. Only those weeds that survive being sprayed with glyphosateherbicides pass on their genes, leading to a steady increase in glyphosate-resistant plants in the weed population.

There is also a second route through which glyphosate-resistant weeds develop: GM crops can pass on their genes for herbicide tolerance to wild or cultivated non-GM relatives. GM canola has been found to pass on its glyphosate-tolerance genes to related wild plants such as wild mustard, turning them into difficult-to-control superweeds. The GM herbicide-tolerance gene was shown to persist in these weed populations over a period of six years.²⁵

GM canola itself has also become a weed. Feral canola populations have acquired resistance to all of the main herbicides used in Canada,²⁶ making it difficult and expensive to control “volunteer” canola in soy and maize fields. Feral herbicide-resistant canola has also become a problem in sugar beet fields in the US, where canola seeds are reported to be deposited by defecation from geese migrating from Canada.²⁷

“Herbicide-resistant crop technology has led to a 239 million kilogram (527 million pound) increase in herbicide use in the United States between 1996 and 2011, while Bt crops have reduced insecticide applications by 56 million kilograms (123 million pounds). Overall, pesticide use increased by an estimated 183 million kgs (404 million pounds), or about 7%.”
– Dr Charles Benbrook, Centre for Sustaining Agriculture and Natural Resources, Washington State University, in a study based on US Department of Agriculture data²

“The promise was that you could use less chemicals and produce a greater yield. But let me tell you none of this is true.”
– Bill Christison, president of the US National Family Farm Coalition²⁸

The GM industry “solution” to superweeds: More herbicides

The industry’s solution to the glyphosate-tolerant superweeds crisis has been first, to aggressively market pre-mixed herbicide products to farmers; and second, to develop stacked-trait GM crop varieties that are resistant to multiple herbicides. These stacked-trait crops enable farmers to spray mixtures of herbicides freely, instead of having to apply them carefully in order to spare crops.¹⁹ Simple logic indicates that this will increase the amount of herbicide applied to any given field.

The chemical and GM seed company Dow has applied to the US government to release its multi-herbicide-tolerant GM soybean, engineered to tolerate being sprayed with glyphosate, glufosinate, and 2,4-D,²⁹ and a 2,4-D-tolerant maize.³⁰

Weed scientists warn that such multi-herbicide-tolerant crops will cause an increase in 2,4-D use, trigger an outbreak of still more intractable weeds resistant to both glyphosate and 2,4-D, and undermine sustainable approaches to weed management.¹

In fact, weed species already exist that are resistant to dicamba,³¹ to 2,4-D,³² and to multiple herbicides.³³ They could be termed stacked-trait superweeds.

Most stacked-trait superweeds emerge through what is known as selection pressure, where only those weeds that can tolerate a herbicide survive to pass on their genes. Others emerge through cross-pollination of GM herbicide-tolerant crops within the crop species or with wild relatives. Stacked-trait multi-herbicide-resistant oilseed rape (canola) plants have already appeared as a result of cross-pollination between GM crops engineered to tolerate different herbicides. The plants are considered weeds because they grow and spread despite the fact that they are not deliberately planted. As early as 1998, oilseed rape plants were found that tolerated up to three different herbicides.³⁴

A Canadian government study showed that after just 4–5 years of commercial growing, GM oilseed rape engineered to tolerate different single herbicides had cross-pollinated to create stacked-trait “escaped” plants resistant to up to three herbicides, posing a serious problem for farmers.²⁶¹⁸

Conclusion

GM herbicide-tolerant crops have led to massive increases in herbicide use (herbicides are a class of pesticide). The small reduction in the use of chemical insecticide sprays due to GM Bt insecticidal crops is swamped by the large increase in herbicide use due to GM herbicide-tolerant crops.

Since GM crops were introduced in the US, overall pesticide use has increased by an estimated 183 million kg (404 million pounds), or about 7%, compared with the amount that would have been used if the same acres had been planted to non-GM crops.

The widespread use of herbicide-tolerant crops has led to the rapid spread of herbicide-resistant superweeds. Farmers have to spray more herbicide, or mixtures of herbicides, to try to control the weeds.

The area of US cropland infested with glyphosate-resistant weeds expanded to 61.2 million acres in 2012. In some areas, farmland has had to be abandoned and farmers have had to resort to pulling weeds by hand.

This “chemical treadmill” model of farming is unsustainable and especially impractical for farmers in the Global South, who cannot afford expensive chemical inputs to control resistant weeds.

References

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