Impact of genetically modified crops: The first 13 years

Impact of genetically modified crops: The first 13 years

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By Charles Benbrook

The trend towards an ever increasing difference between the volume of herbicides used to control weeds in fields cultivated with RH varieties compared to fields cultivated with conventional seeds is due to two main factors: The appearance and rapid expansion of glyphosate resistant weeds and increasing reductions in the volume of herbicides applied in the cultivated area with non-GM varieties.

Between 2006 and 2008, 381 million hectares of herbicide-resistant (RH) genetically modified (GM) corn, soybeans and cotton were cultivated in the US. RH soy represented two thirds of this area.

145 million hectares of GM insecticidal (Bt) cotton and corn varieties have also been cultivated, with corn representing 79% of this area.

Counting the area sown for each of these traits, between 1996 and 2008, about 526 million hectares of RH and Bt crops (hectares / trait) would have been cultivated, with HT crops representing 72% of this area. The actual area planted with GM soybeans, corn and cotton in this period, however, is considerably less than 526 million, due to the predominance of corn and cotton varieties that exhibit both transgenic traits.

Impact on the use of pesticides

In the first 13 years of use on a commercial scale, GM crops have increased the total use of pesticides by 144.4 million kilos compared to the amount of these products that would surely have been applied if RH and Bt seeds were not available.

This increase of 144.4 million kilos represents an average of 0.28 additional kilos of active ingredient pesticide per hectare / GM trait planted in the first 13 years of growing transgenic varieties on a commercial scale.

During this same period, Bt corn and cotton have achieved reductions in the use of insecticides that amount to a total of 29.1 million kilos. The use of Bt corn has reduced the use of insecticides by 14.8 million kilos, that is, around 0.1 kilos per hectare, while Bt cotton has reduced the use of insecticides by 14.3 million kilos, that is say about 0.4 kilos per hectare.

During the 13 years of cultivation, RH crops have increased the use of herbicides by 173.5 million kilos. Of this total, RH soybeans have increased herbicide use by 159 million kilos (about 0.62 kilos per hectare), representing 92% of the total increase in herbicide use in the three RH crops.

The use of herbicides in the cultivated area with RH varieties has recently experienced a very marked increase, with the increase in the use of herbicides in the 2007 and 2008 seasons representing 46% of the total increase of the three crops in these 13 years. From 2007 to 2008 the use of herbicides in RH crops increased by a significant 31.4%.

In the first three years of commercial-scale cultivation (1996-1998), GM varieties achieved an annual reduction of pesticides used in agriculture of 1.2%, 2.3% and 2.3%, but in 2007 there were increased its use by 20%, and in 2008 by 27%.

This trend towards an ever increasing difference between the volume of herbicides used to control weeds in fields cultivated with RH varieties compared to fields cultivated with conventional seeds, is due to two main factors

The appearance and rapid expansion of glyphosate resistant weeds and increasing reductions in the volume of herbicides applied to the area cultivated with non-GM varieties.

Resistant weeds

The widespread adoption of RoundupReady (RR) cotton, corn and soy resistant to glyphosate (RG) has greatly increased the use of products with this herbicidal component. Excessive dependence on glyphosate has generated a growing infestation of weeds resistant to this herbicidal compound, just as an excessive use of antibiotics can cause the proliferation of bacteria resistant to antibiotics.

RG weeds were virtually unknown before the introduction of RR crops in 1996. Today, however, at least nine RG weeds infest millions of hectares of US agricultural land. Thousands of fields are home to two or more resistant weeds. This problem is hitting the southern counties the hardest, although it is spreading rapidly to the Midwest and northern US, to Minnesota, Wisconsin and Michigan. In general, farmers have five options for responding to resistant weeds in fields planted with RH crops:

  • Apply additional herbicides,
  • Increase the dosage of the herbicide (or herbicides) used,
  • Perform multiple applications of herbicides that were previously only applied once,
  • Increase tillage for weed control, or
  • Remove weeds manually.

In the period covered by this report, the first three have been by far the most common responses, thus increasing the volume of herbicides applied to the area sown with RH varieties.

Glyphosate-resistant amaranth (Amaranthus palmeri) has spread dramatically across the southern US since the first resistant populations were confirmed in 2005, and already represents a major threat to US cotton production. In some cases the degree of infestation is so severe that cotton growers have been forced to abandon the land or to resort to the pre-industrial practice of mechanically removing weeds with a hae.

The hardy coniza (Conyza canadensis) is the most widespread glyphosate-resistant weed. It first appeared in Delaware in 2000, and has now invaded several million acres in at least 16 southern and midwestern states, most notably Illinois. The proliferation of coniza and eight other glyphosate-resistant weeds is not only causing considerable increases in the use of glyphosate, but also an increase in the use of more toxic herbicides, including paraquat and 2,4D, a component of the Agent Orange used in the Viet Nam war as a defoliant product.

In the foreseeable future, an increasing reliance on older and higher risk herbicides for the management of resistant weeds in RH crops is now inevitable, which will significantly increase the ecological and health footprint of weed management in more than 40 million hectares of land. agricultural area in the US. This footprint will increase and become more diverse, encompassing an increasing risk of birth defects and other reproductive problems, more serious impacts on aquatic ecosystems, and much more frequent episodes of herbicide damage to vegetation and crops near RH fields. due to unintended dispersal of the herbicide in the environment.

Graph 1.1. shows the upward trend of the kilos of glyphosate applied annually for each of the three RH crops. Data from the US Department of Agriculture's National Agricultural Statistics Service (USDA NASS) show that since 1996 the amount applied per growing season has tripled on cotton farms, doubled in the case of soybeans and increased 39% in corn. The average annual increase of kilos of glyphosate applied per hectare in cotton, soybeans and corn has been 18.2%, 9.8% and 4.3% respectively since the introduction of the RH crops.

Use of lower doses of herbicides in conventional crops

The second key factor that has led to a growing margin of difference in the use of herbicides in RH crops compared to conventional crops, is the advancement of the herbicide industry in the discovery of more potent active components, whose efficacy allows an application in smaller and smaller quantities. As a result of these advances, the volume of herbicides per hectare used in conventional crops has declined steadily since 1996. In contrast, glyphosate / Roundup is a herbicide that requires relatively high-dose applications, and the volume used of Glyphosate has increased rapidly in the acreage planted with RH crops, as is evident from the NASS data presented above.

The volume of herbicides applied to conventional soybean crops decreased from 1.3 kg of active ingredient per hectare in 1996 to 0.55 kg in 2008. The constant reduction in the volume of herbicide applied to conventional soybean represents approximately half of the Difference in herbicide use in GM soybean crops compared to conventional ones. The increase in the volume of herbicides applied to RH soybean crops, from 1 kg in 1996 to 1.85 kg in 2008, represents the other half of the difference.

A similar trend has been recorded for insecticides. The volume of insecticides applied to control the corn rootworm (Diabrotica virgifera) amounted to about 0.8 kilograms per hectare in the mid-1990s and about 0.2 kilograms a decade later. The exception to this rule of spectacular fall in the volume of pesticides used are the insecticides used to control the heliotis / cotton worm complex (Helicoverpa armigera / H. Zea), having decreased in this case marginally, from 0.62 kilos to 0.53 kilos per hectare.

The future of GM corn, soybeans and cotton

In 2010 the vast majority of corn, soybeans and cotton grown in the US will be planted with GM seeds. This prediction is far from being bold, as the supply of non-GM seed is currently so scarce that most farmers will have to buy GM seeds for years to come, whether they want to or not.

If the current trend continues, the GM corn, soybean and cotton seeds planted in the next 5 to 10 years will have incorporated an increasing number of transgenic traits (usually 3 or more), their price per hectare will be considerably higher, and They will pose exceptional resistance management, plant health, food safety and ecological risks. The RH crops will continue to generate an increase in the use of herbicides, and this increase will continue to exceed in the future the reduction in the use of insecticides achieved in the Bt crops.

A turning point in RoundupReady (RR) crops

The year 2009 will probably mark several turning points in the trend of RR crops. RH soybean acreage decreased 1% from the previous year, and will likely drop several additional percentage points again in 2010. In several states, demand for conventional soybeans is outpacing supply, prompting universities to work with companies regional seedbeds to try to cover this lack.

Reasons argued by farmers for abandoning the RR system include the cost and problems inherent in controlling glyphosate resistant weeds, the rapid increase in the price of seeds, the advantageous selling prices of non-GM soybeans, a yield of RR2 soybeans lower than expected and promised in 2009, and the possibility of saving and replanting conventional seeds (a traditional practice that the purchase of RH / RR seeds makes illegal).

In regions where farmers are already fighting resistant weeds, especially amaranth (Amaranthus palmeris) and coniza (Conyza canadensis), university experts project increases of up to $ 200 per hectare in costs associated with RH crops in 2010. This The increase represents a substantial 28% of revenue per hectare of soybeans relative to costs, based on USDA's optimistic 2010 soybean revenue forecast (median yield 42 bushels; median price, about $ 9.90). .

The economic outlook is much bleaker for farmers with average soy yields (36 bushels) and sales price ($ 6.50 per bushel) struggling to combat herbicide-resistant weeds. This type of average conditions will generate around 578 dollars of gross rent per hectare. The increase in costs per hectare of $ 198 estimated for RH soybeans would represent in this case a third of the gross income per hectare, with total operating costs exceeding $ 494 per hectare, leaving only $ 84 to cover expenses. of labor, management, interest, land and other fixed costs. Such a scenario leaves little or no profit margin for the farmer.

Resistance management remains key to maintaining the efficacy of Bt crops

The future of transgenic Bt crops is more promising, but only as long as the emergence of resistance is avoided. The seed industry, the Environmental Protection Agency (EPA), and university scientists have collaborated effectively for the past 13 years, striving to closely monitor and prevent the emergence of insect populations resistant to Bt crops.

But nowadays some experts argue that resistance prevention measures in Bt crops can be relaxed, pointing out that the tendency of the seed industry to incorporate several Bt toxins to the same variety of corn or cotton should reduce the risk of this appearance. trouble. Apparently this argument has convinced the EPA, since it has recently authorized the commercialization of several Bt crops with much less strict provisions on management for resistance prevention.

Experience indicates that it is premature to decrease the attention devoted to the prevention of resistance. It took 10-15 years for insects that damage corn and cotton to develop resistance to each of the new types of insecticide used for pest control.

Bt cotton has been in cultivation for 14 years now, but the area planted did not reach a third of the total cotton crop until 2000. Furthermore, in 2003, around just when experts had predicted that resistance would appear in the field, the first were discovered Cotton worm (H. zea) populations resistant to Bt in cotton fields in Mississippi and Arkansas in 2003.

The Bt varieties for control of the corn rootworm have been planted in a significant area for only 3 years (2007-2009), while the hybrids of Bt corn for control of the eastern borer still occupy only slightly more than half of the national surface. For both types of Bt maize, and especially in the case of Bt maize for rootworm control, it is too early to say with any degree of confidence that the emergence of resistance is no longer a significant risk.

Future trends

So far agricultural biotech companies have devoted the lion's share of their R&D resources to developing just two biotech traits: herbicide tolerance and insect resistance. Pest control systems based primarily on these two characteristics are in danger, biologically and economically, for the simple reason that they foster an almost exclusive reliance on single-component strategies - season after season, year after year, and on very large areas of crops. These conditions represent a "perfect storm" for the evolution and spread of resistance.

No one seriously questions that RR crops have become very popular, for the most part effective, and almost budget neutral for farmers. But they have promoted an unprecedented reliance on glyphosate for weed control, and this over-reliance has generated a growing infestation of glyphosate-tolerant and resistant weeds.

Two of the main players in this industry - Monsanto and Syngenta - currently offer farmers discounts of the order of $ 30 per hectare for spraying with herbicides whose components act differently from glyphosate. Monsanto's program will even pay farmers to buy herbicides sold by competitors, indicating the extent to which Monsanto perceives the threat hanging over its most profitable production lines to be very serious.

While the expansion of resistant weeds is a predicted catastrophe that undermines their bottom line for corn, soybean and cotton growers, the seed and pesticide industry sees new market and profit opportunities following the emergence of resistant weeds . Much of the industry's investment in R&D is going into developing new crops that will withstand higher doses of glyphosate, or that will tolerate additional herbicide applications, or both. In short, the industry response is more of the same.

A major biotech company has filed and successfully applied for a patent on RH crops that can be sprayed with products from seven or more different families of chemical herbicides. These next generations of RH crops will probably be fumigated with two or three times the number of herbicides applied routinely today in fields planted with RH varieties, which will continue to increase the total volume of herbicides applied to these types of crops, as well as the cost of herbicides.

This approach to the problem of the rapid emergence of herbicide-resistant weeds is as crazy as spraying gasoline on a fire in the hope of smothering the flames.

Rather than spraying more, farmers should diversify their weed management tactics, modify crop rotations, scrupulously follow recommended herbicide resistance management plans, and more aggressively use tillage to bury seed tolerant to weeds. herbicides deep enough to prevent germination.

The most pressing immediate goals for farmers, scientists, and the seed industry include developing weed management systems capable of getting ahead of resistant weeds, ensuring that the commitment to preserve the efficacy of Bt toxins is not reversed, and expand the supply and quality of conventional corn, soybean and cotton seeds. This last objective will probably end up being the most fundamental, since the productivity of our agricultural system and the quality of much of our food supply begins with and depends on seeds.

* N. de la R. This is the Executive Summary of the report “Impacts of genetically modified crops on the use of pesticides: the first thirteen years”, which was written by Charles benbrook, Ph.D., scientific director of The Organic Center in November 2009 - Translated by Isabel Bermejo and published by RAP-AL Uruguay.

To access the full document (in English) click here:

Video: Genetically Modified Organism GMO (May 2022).


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