Science in Society Archive

GM Crops Increase Herbicide Use in the United States

The use of toxic herbicides on the rise due to the spread of herbicide tolerant crops. Brett Cherry

The rapid rise in herbicide tolerant (HT) crops is increasing the application of toxic herbicides to alarming levels in the US, according to a comprehensive report [1] by the Organic Food Center, USA. Research based on statistics from the US Department of Agriculture (USDA) revealed that from 1996 to 2008 pesticide use increased by 318 million pounds; a decrease of 64 million pounds in insecticide use [1] was overwhelmed by an increase of 383 million pounds in herbicide use [2]. Especially worrying is that most of this increase (46 percent) took place between 2007 and 2008. This has led to major environmental concerns regarding the safety of HT crops as they continue to dominate the corn, soybean and cotton markets in the US. Ecological risks, such as herbicide resistant “super weeds,” and economic impacts on farmers, were especially highlighted in the report released jointly with the Union of Concerned Scientists and the Center for Food Safety, both also in the US. 

HT crops widespread

Data from the US National Agriculture Statistics Service (NASS) indicate that  between 1996 and 2008, farmers planted 941 million acres of HT corn, soybeans and cotton, with HT soybeans accounting for 72 percent of total GM acres planted (see Tables 1a and 1b [2]. GM soybeans alone accounted for 92 percent of the increase in herbicide use. Despite a decrease in the use of insecticides for Bt corn and cotton, the drastic rise in the use of herbicides has led to an unprecedented increase in pesticide use overall.

Table 1a Total acres of HT corn, soybeans and cotton planted, 1996-2003 [1]

Table 1b Total acres of HT Corn, soybeans and cotton planted, 2004-2008 [1]

In 2008, GM crops required over 26 percent more pounds of pesticides per acre than conventional crops [1]. If this trend continues, the report warns that farmers will continue to be plagued by herbicide-resistant weeds and higher costs for GM seeds, not to mention a greater risk to public health (see later). GM corn seed prices could be three times the cost of conventional seeds [2] and it has become more difficult for farmers in the US to buy non-GM seeds since GM corn has dominated the US market [2].  In 2009, the cost of GE corn seed cost farmers between 19 and 34 percent of their gross income and operating costs per acre [3]. The false promises of GM companies to increase yields and reduce costs with GM seeds have failed farmers in the US, resulting in economic exploitation and rising GM seed prices. Farmers who plant GM soybeans will also pay extremely high prices for GM seeds, especially for Monsanto’s new Roundup Ready 2 (RR 2) soybeans that cost $70 per bag, reflecting a 143 percent increase in the price of GM seed since 2001 [3].

US farmers are not alone in witnessing the hazardous impacts of GM seeds on their livelihoods. Farmers in India were promised increased yields from Bt cotton seed, but they never came (see [4] Farmer Suicides and Bt Cotton Nightmare Unfolding in India, SiS 45). Instead, they have suffered even worse from rising Bt cotton seed prices that increased their indebtedness and mass suicides.

HT crops mean more herbicides

The greatest danger in cultivating HT crops is that they can tolerate large amounts of glyphosate in addition to other herbicides, and increasingly more so over time (see Table 2). In comparison, the amount of pesticides applied to non-GM crops has been decreasing, and usually less per acre than GM crops, except for corn prior to 2006 (see Table 3). Since then, the amount of pesticides applied to non-GM corn is less than that applied to HT corn.

Table 2 Average pesticide use per acre for corn, soybean and cotton, 2003-2008 and total pounds of pesticides applied, 1996-2008 [1]

Table 3 Average pesticide pounds (active ingredient) applied per acre for conventional and HT varieties, 1996-2008 [1]

More herbicides mean superweeds and yet more herbicides

The application of more glyphosate herbicides has brought ecological disasters, especially in herbicide resistant superweeds. As weeds become more resistant to glyphosate, farmers apply more or spray multiple herbicides at once. The report comments that “addressing the rapidly emerging problem of resistant weeds in this way makes as much sense as pouring gasoline on a fire in the hope of snuffing out the flames [1].” Due to an increase in herbicide applications, new infestations of glyphosate resistant plants such as pigweed (Palmer amaranth) and horseweed (marestail) have become widespread [2].  In order to kill glyphosate resistant weeds, other toxic and deadly herbicides such as paraquat (N,N′-dimethyl-4,4′-bipyridinium dichloride) and 2,4-D (2,4-Dichlorophenoxyacetic acid) are used. Paraquat has been linked to Parkinson’s disease and is forbidden by the EU, while 2,4-D  is a well known component of the highly toxic defoliant Agent Orange used during the Vietnam War. In light of their impacts on public health, these pesticides should be banned altogether rather than be used to compensate for weed resistance due to the over use of glyphosate. 

The planting of HT crops has made the US the “resistant weed epicentre of the world” with 125 resistant biotypes of 68 weeds, infesting up to 18 million acres, and probably much higher [2]. According to the Weed Science Society of America (WSSA), populations of glyphosate resistant weeds have risen 2.4 million acres in 2007 to 5.4 million acres by early 2009, correlating with increased use of glyphosate herbicides. Since 1996, the application of glyphosate per crop year has tripled for cotton and doubled for soybeans, with an annual increase of 18.2 percent for cotton, 9.8 percent for soybeans and 4.3 percent for corn. 

More independent data needed

Private data on pesticide use can be easily manipulated by biotech companies, making the need for independent data collection imperative for understanding the environmental impacts of GM crops and pesticide use. NASS began making less frequent annual surveys of different field crops since 2002. Due to cuts in funding by the Bush administration, NASS did not collect pesticide use data for 2008 and data collection was limited to cotton and apples in 2007. In order to make up for these shortcomings, the Organic Center had to base their results on estimates using the formula in Box 1 [2]

Box 1

Let H(HT) be the average amount of herbicide per acre applied to HT varieties of a given crop and let H(non-HT) be the average amount of herbicide applied to non-HT varieties of the same crop.  If p is the number of acres on which HT varieties of the crop are grown and q is the number of acres on which non-HT varieties are grown, then the average herbicide used per acre on the crop is

                        p × H(HT) + q × H(non-HT)
                                           p + q                  

The average rate of herbicides for conventional crops was subtracted from the average rate of herbicides applied to GM crops to determine whether herbicide use rose or fell for a particular year (see Table 3) [2]. Other data in the report from the USDA Agricultural Marketing Service (AMS) and the Economic Research Service (ERS) are used to calculate the percentage of acres planted to HT crops [2]. NASS pesticide use data were not available for cotton in 2002, 2004 and 2006; for corn in 2004 and 2006; and for soybeans in 2003 [5], and estimates had to be made. Averages derived from statistical analyses are no substitute for empirical data. In the US, not only universities and environmental groups depend on NASS data, but also the farming industry and the EPA use the data to set pesticide health levels. 

Critics of the Organic Center report who are also consultants for biotech firms, such as PG Economics, UK, rely on surveys by Dmrkynetec (Doane Marketing Research), a US private research firm that supplies pesticide use data for the biotech industry. 

From 2004 to 2007, the Dmrkynetec data show a greater increase in herbicide use for conventional crops despite the adoption of low-dose herbicides by farmers according to NASS data [1]. The Dmrkynetec data also show an increase in herbicide use for HT crops from 1998 to 2004 referred to in a report by PG Economics [6]. Yet PG Economics did not acknowledge the increase, claiming it was not “a reasonable representation” of average herbicide use for HT crops compared to conventional crops [2].

In criticising the Organic Center Report, PG Economics accuses it of overstating herbicide use on HT crops by 63.4 million pounds of active ingredient [7]. It then goes on to refer to its “peer reviewed analysis” that GM crops have reduced herbicide consumption. PG Economics does not refer to data from NASS, a US government agency, but uses only data from Dmrkynetec, which PG Economics claims is the [7] “only comprehensive source of pesticide use data.”  

Not only is Dmrkyntec a marketing research firm, it also places limits on how its data can be released publicly and does not reveal its data collecting methods, making the data worthless for scientific research [8]. 

There are also other questionable sources of data on pesticide use on HT crops that biotech companies cite in their public relations campaigns through the National Center for Food and Agriculture Policy (NCFAP), USA. 

The NCFAP, partly funded by the biotech industry, determines the amount of pesticides used according to pest management systems recommended by university scientists [2]. The problem with this approach is that it does not reflect the pest management systems that farmers actually use. 

Thus, NCFAP reports that 3.23 pounds per acre of herbicides was applied to conventional corn consisting of a mixture of 3.16 pounds of ‘pre-emergent’ and 0.07 ‘post-emergent’ mix of s-metolachlor/atrazine [2]. NASS, which sends enumerators out into the field to observe the amounts of pesticides farmers actually spray [8], reports that conventional corn in 2005 had a combined average rate of no more than 2.48 pounds per acre, not 3.23 [2]. Using NCFAP’s herbicide rates for conventional corn (3.23) and RR corn (2.5) gives a decrease of 0.73 pounds per acre, instead of a slight increase of 0.02 pounds according to NASS data [2]. In the case of RR soybeans, NASS data reveal pesticide applications to be 28 percent higher than the NCFAP estimates [2].

If scientists and farmers are to understand the actual impacts of GM crops on pesticide use they need access to data provided by NASS or other independent sources. Private marketing research firms such as Dmrykynetec cannot serve the public, especially with a price tag of $500 000 per year [8].     

New ‘stacked’ GM seeds

As glyphosate resistant weeds continue to spread rapidly, chemical companies are capitalising on this opportunity by attempting to introduce other pesticides into the market and toxic genes into GM crops. Already many crops have both HT and toxic Bacillus thuringiensis (Bt) traits stacked together. Two Bt genes were used for pests, such as the European corn borer and the corn root worm.  These double and triple-stacked versions made up 57 million acres of corn in 2008 compared to around 14 million acres with single traits, most of which were HT [2]. Bt was found to be highly toxic to cattle who died after eating Bt maize (see [9] Cows Ate GM Maize & Died, SiS 21), and one of Monsanto’s patented Bt corn seeds, MON810, is banned by many countries in the EU (see [10, 11] Acceptance of GM Crops Exaggerated, SiS 42; Europe Holds the Key to a GM-Free World, 5th Conference of GM-Free Regions, Food & Democracy, SiS 43).

The marketing strategy of chemical companies such as Monsanto and Dow AgroSciences to introduce multiple toxic traits into GM crops is called “biotech trait penetration” [1]. In GM crop markets, farmers must pay a fee per trait, so instead of relying on single trait varieties they must pay for multiple traits within the same crop. According to the report, Monsanto and Dow AgroSciences will replace their triple stack GM seeds with an eight GE (genetically engineered) trait product called “SmartStax” by 2010, in their attempt to create a “captive consumer base” [2] where farmers are backed into the corner of the GM market. SmartStax corn, for example, will cost farmers more than twice as much as conventional seeds [3]. Farmers will be paying the high ‘technology’ costs for seeds plus proprietary herbicides to corporation-conglomerates that will also control the price of the agricultural commodities market, keeping it as low as possible.

Ban toxic herbicides and restore agriculture to the public

Multiple studies reveal that increased pesticide use and the planting of more GM crops is a deadly combination. Public health risks due to GM crops’ tolerance to glyphosate, for example, are worsened by the presence of adjuvants in Monsanto’s Roundup herbicide formulations (see [12] Death By Multiple Poisoning, Glyphosate and Roundup, SiS 42) and recent evidence has confirmed that exposure to Roundup disrupts sex hormones (see [13] Ban Glyphosate Herbicides Now, SiS 43). Argentina has considered banning glyphosate herbicides after researchers found it could cause birth defects (see [14] Glyphosate Herbicide Could Cause Birth Defects, SiS 43). 

If chemical companies such as Monsanto are allowed to continue to monopolise agriculture, conventional plant breeding programs will become obsolete. While endangering public health and ecology, over dependence on toxic herbicides is also depriving the world of one of its most precious resources, traditional, low-tech farming practices. This can be restored by investing in organic agriculture that has been shown to increase yields and produce more nutritious food (see [15] UK Food Standards Agency Study Proves Organic Food Is Better, SiS 44) without the use of any pesticides. 

Furthermore, in patenting GM seeds and forcing them onto farmers, biotech companies are attempting to control our food supply. The future of agriculture lies with organic, non-GM methods that can feed the world in the developing and developed world (see [16] Food Futures Now: *Organic *Sustainable *Fossil Fuel Free). 

Article first published 18/01/10


  1. Gillam C. Biotech crops cause big jump in pesticide use: report. 17 November 2009. Reuters.     
  2. Benbrook C. Impacts of genetically engineered crops on pesticide use: the first thirteen years. The Organic Center. 2009 November.
  3. Benbrook C. Critical issue report: the seed price premium. The Organic Center. 2009 December.
  4. Ho MW. Farmer suicides and Bt cotton nightmare unfolding in india. Science in Society 45
  5. National Agriculture Statistics Service. Agriculture and chemical usage – field crops 19 March 1992 to 21 May 2008. 5 January 2010. USDA
  6. Brookes G and Barefoot P. “Gm crops: global socio-economic and environmental impacts 1996-2007,” PG Economics Ltd, Dorchester, UK.
  7. PG Economics Limited. Impact of genetically engineered crops on pesticide use: us organic center report evaluation by pg economics. 19 November 2009.
  8. Engelhaupt, Erika. Government pesticide and fertilizer data dropped. Environ. Sci. Technol. 2008, 42, 6779–6780
  9. 9. Ho MW. Cows ate GM maize & died, Science in Society 21,4, 2009
  10. Cherry B. Acceptance of gm crops exaggerated. Science in Society 42, 11, 2009
  11. Ho MW. Europe holds the key to a gm-free world, 5th conference of gm-free regions, food & democracy. Science in Society 43, 21, 2009
  12. Ho MW and Cherry B. Death by multiple poisoning, glyphosate and Roundup. Science in Society 42 , 14, 2009
  13. Ho MW. Ban glyphosate herbicides now. Science in Society 43, 34, 2000
  14. Ho MW. Glyphosate herbicide could cause birth defects. Science in Society 43, 36, 2009
  15. Ho MW. UK food standards agency study proves organic food is better. Science in Society 44, 32, 2009
  16. Ho MW, Burcher S, Lim LC, et al. Food Futures Now, Organic, Sustainable, Fossil Fuel Free, ISIS and TWN, London, 2008.

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There are 6 comments on this article so far. Add your comment above.

R. K. S. Rathore Comment left 6th March 2010 19:07:11
Use of Glyphosate to remove weeds is a very handy tool, if it harms the fertility of soil we have to think in terms of sustainable Agriculture? Promotors of Glyphosate use should come out with specific information. The world is facing shortage of food grains. Use of Glyphosate effectively controls weed and help in more productivity per unit area with lesser amount of water. Before we reject or blame the HT crops and Glyphosate theoretically, we should have enough data to do so.

Brett Comment left 21st January 2010 02:02:35
Yes. There is certainly data showing how HT crops and glyphosate have adversely impacted soil microbial communities and have increased the presence of toxic fungi in the soil, not to mention potential leaching into ground water and bodies of water nearby. Other populations of microorganisms are affected as well. Glyphosate is definitely not 'benign' in this sense at all. There are groups of researchers investigating these impacts, perhaps more than what tends to be heard of in the US, due to the pro-GM lobby. We will be reporting on this in the near future. Stay tuned.

John Wilson Comment left 20th January 2010 04:04:31
It would be interesting to know what is happening to the fertility of the soil in which HT GM crops are grown. I suspect that yearly applications of glyphosate herbicides will gradually reduce soil fertility. There is evidence that mycorrhizal fungi, nitrogen fixing bacteria and earthworms are harmed by Roundup. Many other vital soil organisms are also likely to be adversely affected by contact with glyphosate herbicide chemicals. Monsanto claim that glyphosate is deactivated on contact with the soil. However there is evidence that glyphosate can stop binding to soil particles and move through the soil in solution. Is anyone investigating this aspect of GM farming ?

Jimmy Comment left 27th January 2010 01:01:55
Why are proponents of organic agriculture concerned with hebicide resisitant weeds. They don't pose any greater threat than any other weed that routinely infests and reduces their yields. Also the Organic Food Centre report bases its herbicide use for non-GM on rates in areas free from HT crops. As these tend to be the areas with very low or no weed pressure (hence HT technology isn't necessary) there is a massive underestimation of the increases directly caused by GM. Finally, what sort of measurement of herbicide use is 'pounds of herbicide' used? Some are highly toxic and will kill a human on exposure (largely now banned) whereas others are less toxic than the coffee you drink or the toothpaste you brush your teeth in. [offensive paragraph edited out]

Richard Comment left 10th November 2012 00:12:07
Jimmy is correct. The LD50 toxicology data on something like 2,4 D mentioned in the above article is almost 10x worse than glyphosate. (LD50 of ~5000mg/kg vs. ~600mg/kg). 2,4 D use went down as glyphosate increased with Round-up ready crops. Even if we used 2x as much glyphosate as 2,4 D, since 2,4 D is fatal at levels 10x less, we would still be 5x safer with glyphosate. It will be interesting to see if facts are deemed an "offensive paragraph" and this is edited out.

George Comment left 26th November 2012 06:06:23
I think you're missing the point Jimmy and Richard. The fact that 2,4 D is more toxic than Glyphosate is a premise for why it shouldn't be used. The point of the article seems that any use of glyphosate will result in harming the environment and people and that it isn't as benign as once thought. Is it safer compared to 2,4D, I don't doubt it, but this doesn't make Glyphosate 'safe' either. What's wrong with herbicide-resistant weeds? Are you joking? Maybe the fact they resist herbicides making them highly difficult to kill requiring more herbicides?