Pesticide Use and Glyphosate Resistant Weeds – a Case Study of Brazilian Soybean Production


Pesticide use and glyphosate resistant weeds – a case study of Brazilian soybean production
By Daniel E. Meyer and Christel Cederberg
Publisher: Swedish Institute for Food and Biotechnology
This study investigates how the use of pesticides in Brazilian soybeans has changed since 2003/2004 when the cultivation of genetically engineered (GE) glyphosate-tolerant soybean cultivars (so-called Roundup Ready (RR) soybeans) started. Also included is an overview of the growing problem of glyphosate-resistant weeds in the world´s soybean fields and its consequences for weed management and herbicide use in present and future soybean production.
Data on pesticides were collected from Brazilian agencies and institutes, and completed with information from recently published scientific literature as well as contacts with Brazilian researchers in the fields of agriculture and environment. A field study was conducted in the state Rio Grande de Sul in June 2010 where farmers were interviewed on herbicide use, motives for choosing GE soybeans and their concerns for glyphosate-resistance weeds.
Brazilian soybean production and GE soy
Brazil is the second largest producer and exporter of soybeans in the world. Planted areas with soybeans have had a strong growth during the last 20 years, from 11.5 million hectares in 1990 to 21.7 million hectares in 2009. Total production for 2009/2010 harvest is estimated at 65 million tons. Five states are responsible for 80% of Brazil´s soybean production; Rio Grande do Sul and Parana in the south (older cultivation areas) and Mato Grosso, Goîas and Mato Grosso do Sul in the center-west (cerrado-region).
GE glyphosate-tolerant soybeans became legal and commercialized later in Brazil than in the U.S. and Argentina. In 2003, RR soybeans were allowed temporarily in the state Rio Grande do Sul and in 2005, the Biosafety Act was passed admitting planting and commercialization of RR soybeans all over Brazil. The technique has had a rapid and widespread adoption and in 2009, around 70 % of soybean acreage was cultivated with GE glyphosate-tolerant soy cultivars.
Pesticide use
Sales and use of pesticides in Brazilian agriculture are large and growing; the expanding soybean crop is responsible for approximately 45 % of all pesticides sold. In 2008, close to 140 500 ton active ingredients
(a.i.) were sold for the soybean crop, corresponding to a national average use of around 6.6 kg total pesticides as a.i. per hectare soybeans. The sales of these pesticides had a total value of a little more than 3 billion US dollar.
Between 2003 and 2008, average herbicide use increased from around 2.8 kg to 4.2 kg a.i. per hectare soybean (50% growth) and in 2008, approximately 1.5 kg herbicides was used to produce 1 ton soybean. In comparison with other major Brazilian crops, herbicide use in soybeans has had a larger growth in the period 2003 – 2008.
Average fungicide use in the soybean crop increased from 0.32 to 0.55 kg a.i. per hectare between 2004 and 2008 (70% growth). In 2008, 0.2 kg a.i. fungicides were used per ton soybean produce. Asian soybean rust is the main fungal disease affecting soybean production in Brazil and this disease, first identified in 2001, is most likely an important explanation to the growing use of fungicides.
The soybean crop contributes to a significant part of use and sales of insecticides, corresponding to around 45% of total. There is a trend towards increasing dependence of insecticides in the soybean crop; in 2004 the average rate was 0.6 kg a.i. per hectare increasing to around 1 kg a.i. per hectare in 2008. The average use of insecticides was 0.39 kg a.i. per ton soybean produce in 2008.
GE soy and glyphosate-resistant weeds
USA, Brazil and Argentina are responsible for close to 80% of world soybean production today and dominate the world exports of soybeans and soymeal. In 2009, 91%, 99% and 71% of total soybean acreage were grown with GE glyphosate-tolerant cultivars in the U.S., Argentina and Brazil respectively. This massive adoption has led to excessive reliance of glyphosate for weed control in world soybean production. Initially, growers adopted the new weed management technique with little reservation since it made weed control easy and cheap and enabled earlier seeding and no-tillage. However, only three years after introduction of RR soybean in the U.S., the first report came of a glyphosate-resistant weed species associated with RR soybeans. In 2010, reports on glyphosate-resistant weeds indicate 30 000 infested sites on up to around 4.6 Mha in the U.S. The development in Brazil and Argentina is less analysed than in the U.S. Recently, the U.S. House Committee on Oversight & Government Reform Subcommittee on Domestic Policy arranged hearings on the growing problems of glyphosate-resistance weed in the North-American agriculture.
Consequences of glyphosate-resistant weeds
Statistics on pesticide sales show that herbicide use in soybeans has increased after adopting the new weed management technique of GE glyphosate-tolerant crops in the U.S. and Brazil. A major cause for the increasing use of herbicides in soybeans is the rapid evolvement of glyphosate-resistant weeds in GE glyphosate-tolerant crops.
Biotech seed makers are responding to the problem by developing new GE herbicide-tolerant crops, i.e. GE crops that are resistant to more herbicides than only glyphosate. Under development are GE crops with genes that confer resistance to herbicides with other mode of actions than glyphosate, for example 2,4-D and dicamba. Weed scientists in the U.S. estimate that these new multi-herbicide-tolerant GE soybeans can lead to a strong growth of herbicide use in the U.S. soybean crop in the coming years. Furthermore, since there has not been any development of new herbicides, a significant proportion of the projected increase will be of older, less environmentally friendly herbicides.
Also in Brazil, there are signs of increased use of older and more toxic herbicides in the soybean crop, for example, imports of the toxic herbicide paraquat have increased strongly the last years and there are reports of growing use of paraquat and 2,4-D in soybean regions.
Herbicide resistant weeds can evolve when there is insufficient diversity in weed management systems. Diversity in weed control methods includes herbicides of different mode of actions, some tillage operations, better crop rotations, use of cover crops etc. Present overall dominance of one single weed management technique in world soybean production – excessive use of glyphosate in GE glyphosate-tolerant cultivars combined with no- or lowtillage – is not beneficial for a diversity of cultivation techniques in soybean. This is a well motivated argument for why alternative cropping systems also should be included in future soybean production.
Concluding remarks
For a period of only a little more than ten years, weed management in world´s soybean fields has changed profoundly as a consequence of the rapid adoption of the new cultivation technique combining GE glyphosate-tolerant cultivars and no-tillage. Today, over 85% of soybean acreage in the three major producing countries (USA, Brazil and Argentina) is cultivated with genetically modified cultivars, foremost Roundup Ready soy. There are no signs that this new weed management technique has resulted in a general reduction of herbicide use in soybeans. In fact, pesticide statistics from the U.S. and Brazil instead point at the opposite. Herbicide use has increased subsequently to the large-scale shift to this new cultivation technique including GE glyphosate-tolerant soy cultivars which have involved a very high reliance on one single herbicide, glyphosate.
The major cause for the increasing use of herbicides in soybeans is the rapid evolvement of glyphosate-resistant weeds in GE glyphosate-tolerant crops (foremost soybean, maize and cotton) and this development disqualifies earlier claims that glyphosate could be used as
(almost) the sole herbicide to manage weed in GE glyphosate-tolerant crop systems.
According to Waltz (2010), Monsanto had an aggressive market campaign in the late 1990s, saying that weeds would not develop resistance to glyphosate if the herbicide was used in right time and at the right rate.
To qualify for the company´s Roundup Reward´s program (a kind of warrantee for crops) at that time, U.S. growers could only use Roundup and certain approved herbicides on Roundup Ready crops. The qualifications for Monsanto´s rewards program has since changed and in autumn 2010, the company launched the Roundup Ready Plus program, paying growers to apply additional herbicides besides glyphosate to hamper the emerging weed-resistant problem. This very different attitude from Monsanto, which has occurred in a period of only some ten years, is a striking sign of the seriousness of the problem with glyphosate-resistant weeds.
The total dominance of the new weed management technique in world soybean production, based on GE glyphosate-tolerant cultivars, has not only contributed to a rapid emergence of glyphosate-resistant weeds. Also, the development of novel herbicides with different mode of actions has slowed substantially in recent years because of little market incentives for companies to discover new herbicides due to the near-monopoly use of glyphosate in GE herbicide-tolerant soybeans (CAST, 2009). The biotech industry response to the problem is now to develop a new generation of GE crops where glyphosate-tolerant cultivars are being engineered to have additional resistance traits introduced in the crop´s genome, see also Table 3 (Waltz 2010). These additional gene inserts will confer resistance to old herbicides, most importantly 2,4-D and dicamba. Mortenssen (2010) estimates that these new multi-herbicidetolerant cultivars can lead to an increase in herbicide use in the US soybean crop of around 70% in a relatively short time. Due to the absence of newly developed herbicides, a significant proportion of the projected increased herbicide use will be older, less environmentally benign compounds (Mortenssen, 2010).
Also in South America, the risk of a growing use and dependence of old and more toxic herbicides as a consequence of the evolving problem of glyphosate-resistance weeds is obvious. However, the potential development in Brazil and Argentina is less analysed than in the U.S. as there are less data and statistics available on trends in pesticide use in South America. For example, in this study we could not find consistent national statistics on how the use of Paraquat-based herbicides has developed in Brazil subsequent to the large-scale adoption of GE glyphosate-tolerant soybeans but there are indications that the use of Paraquat will increase as a consequence of the development of glyphosate resistant weeds.
Concerning this particular substance, there is an obvious double standard of morality worth calling attention to. Paraquat has not been allowed to use in the EU since 2007 due to its acute toxicity and European farm workers and environment thus now avoid the exposure to this toxic chemical. In the last few years, European exports of Paraquat dichloride to Brazil have developed from zero in 2007 to 2.8 million kg in 2008 and 6.6 million kg in 200919. Since the EU is one of the major importers of Brazilian soy products, European protein feed suppliers, not making demands on the use of toxic chemicals in their feed supply chain, can continue to benefit from relatively cheap soymeal while the risks of handling and using chemicals such as Paraquat, are transferred away from European farm-workers and environment to the other side of the Atlantic Ocean. The growing use of Paraquat is also noteworthy as it is one of 14 substances that ANVISA recently planned to re-evaluate, a process that was stopped due to court decisions, supposedly base on files from the chemical industry.
The soybean fields in the Americas are the pre-dominant protein source of world´s pork and poultry production. Successful weed management is important for soybean yields and choices of cultivation technique affect important environmental impacts such as soil erosion and pesticide residuals in soil, water and air. As the soybean crop is significant and strategic for present and future food production, it is a general interest that weed control systems in the crop are developed for long-term sustainability, securing stable yield levels and minimizing extern environmental impact. Also the herbicide glyphosate, regarded as the world´s most important herbicide, must be used in a responsible way ensuring its long-term effect in future weed control.
The rapid and large-scale adoption of GE glyphosate-tolerant soybeans has led to consequences that can threaten long-term sustainability in soybean weed management. The almost exclusive use of one single herbicide has in short time led to the evolving of several glyphosate-resistant weed species, many of which are troublesome weeds in agriculture.
Development of weed management methods in the soybean crop during the last 20 years has had a one-sided focus on the GE technique and glyphosate as the single herbicide. This has prevented the progress of new herbicides that now are needed to control problem-weeds and address the weed resistance concerns. In the U.S., few non-GE soy varieties are being developed by the seed companies since the growers´ demand have foremost been for GE glyphosate-tolerant varieties.
Herbicide resistant weeds can evolve when there is insufficient diversity in weed management systems. Diversity in weed control methods includes herbicides of different mode of actions, some tillage operations, better crop rotations, use of cover crops etc. Present overall dominance of one single weed management technique in world soybean production – glyphosate dominance in GE glyphosate-tolerant cultivars combined with no- or low-tillage – is not beneficial for a diversity of cultivation techniques in soybean crops. This is a well motivated argument for why also alternative cropping systems, conventional and organic, should be developed for future soybean production.
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