Issue:

Does the Use of Genetically Engineered Crops Result in Decreased Use of Pesticides?

Response:

Having crops tolerant to herbicides and pest attack increases pest management options and can also reduce the number and strength of pesticide applications. Growth of GE HT crops also allows topical application of herbicides to crops and weeds, which replaces spraying between crop rows and mechanical removal of weeds, both of which can damage crops and result in environmental damage. Reducing mechanical tillage lowers fuel consumption and helps conserve soils prone to erosion and compaction (1). HT crops can also lead to more flexible herbicide treatment regimes.

Herbicide usage on HT GE crops has been analyzed in numerous studies. The National Center for Food and Agricultural Policy (NCFAP) published surveys in 2000, 2003, and 2004 on U.S. pesticide usage on GE crops by collecting information from industry experts, academic researchers, and Cooperative Extension. In 2004, HT canola, cotton, maize, and soybean, as well as Bt cotton and maize, were studied; reductions in herbicide active ingredient (AI) were 25 to 33% (2). In a 2006 publication, the USDA National Agricultural Statistics Service (NASS) looked at both herbicide and insecticide use, analyzing data up to 2002. AI use rates for HT cotton and corn and Bt corn declined from 1996 to 2002 (figure 8 in Reference 3); overall reductions in pesticide (herbicide+insecticide) use were observed as adoption of Bt and HT cotton, corn, and soybeans increased. This phenomenon led to an overall reduction of ca. 2.5 million pounds of AI, although slight increases in herbicide use with soybeans were found (4). The latter increase is consistent with the fact that, as glyphosate application to HT soybean acreage increased, concurrent shifts occurred toward less environmentally persistent herbicides (figure 2 in Reference 5), such as pendimethalin, trifluralin, and metolachlor (6). Taken together, these results agree with many field tests and farm surveys showing lower pesticide use for GE versus conventional crops (table 3 in Reference 3).

Using the same data from USDA NASS and other experts and extrapolating from trends when data were missing, another study also found higher glyphosate use from 2002 to 2004 on HT soybean compared with its use on conventional soybean but no increase from 1996 to 2001 (7). The increase in use from 2002 to 2004 was due in part to a switch to more effective herbicide mixtures and to more restrictive policies on herbicide use (5). Similar conclusions were drawn for HT maize. For Bt cotton, a trend was noted toward lower insecticide rates on conventional cotton, due in part to single Bt varieties needing bollworm directed sprays late in the season. Lower pesticide use rates were observed for Bt maize; however, only part of conventional U.S. maize is normally treated with insecticides. The rate decreased in successive years, likely because of use of lower-rate insecticides such as cyfluthrin (7). A more promising approach for pesticide reduction for corn was the introduction in 2003 of a GE variety expressing a modified Cry3Bb1 protein (8), which protects against the western corn rootworm (Diabrotica virgifera virgifera), a difficult-to-control soil pest with a serious economic impact (9).To control rootworm, pesticides are often applied even when its presence is not known, because the economic impact of the pest is often not known until treatment is no longer effective; losses from rootworm damage are often high. Environmental implications regarding adoption of this variety should be considered; these include ecological effects on surrounding soils and the potential for rootworm to develop resistance (10).

The reason all reports on pesticide usage do not reach the same conclusions relates to the use of different data sets and/or different ways of calculating pesticide use (11). Disagreement exists on which methods are most accurate to calculate use rates, because they each reveal different aspects of herbicide usage. Regardless, certain parameters, such as agricultural practices used on and environmental conditions of the acreages compared, should be similar when comparing use rates.

Measuring amounts of pesticide AI used is helpful, but it does not provide adequate data on environmental effects (1), because each pesticide has different environmental and toxicological impacts. One means to take these factors into account uses the concept of an Environmental Impact Quotient (EIQ) (12). EIQ measures environmental and toxicological effects on the basis of many variables: toxicity of the AI, its mode of action, period of time AI persists, and ability of herbicide to contaminate groundwater. Each AI in a pesticide has a specific EIQ based on these parameters.

An EIQ Field Use Rating is determined by multiplying the EIQ value by (a) the amount of AI in a given amount of herbicidal product and (b) the amount of herbicidal product applied per acre. The smaller the EIQ Field Use Rating number, the smaller its environmental impact. By calculating EIQ Field Use Rates for each pesticide, impacts of different pesticides can be compared. EIQs can also be calculated for farm worker health, consumer health, and ecology (5).

In 2006 the environmental impact (EI) of cotton varieties expressing Cry1Ac and Cry2Ab was determined (13). Measurements of Bt protein expression, plant biomass, insecticide application rates, AI measurements, and insecticide EIQ values were used to produce an EI value, expressed as kilograms (kg) AI per hectare for conventional, single-gene, and two-gene Bt cotton from 2002 to 2003 and from 2003 to 2004. The average insecticide EI for conventional cotton was 135 kg AI/ha; for the two-gene Bt variety this value was 28 kg AI/ha as a result of changes in both approach to insecticidal applications and reduction in usage. From 1997 to 2004 in Australia theEIQmethod was used to study the EI of Bt cotton (the single-trait variety Cry1Ac and the double-trait varieties Cry1Ac and Cry2Ab) (13). Pesticidal residues from the plant were also considered but had little effect on overall conclusions. Bt cotton had less EI than conventional cotton; the EI of Cry1Ac cotton was 53% that of conventional, whereas the value for the two-trait variety was 23%. In Canada, HT canola varieties, i.e., glyphosate-, glufosinate- and imidazolinone-tolerant varieties (see “What Methods Are Used to Help Plants Protect Themselves Against Pests?”), have been cultivated on a large scale since their introduction in 1996. The EI of HT canola was determined from 1995 to 2000 using EIQ. Although HT canola acreage increased from10%in 1996 to80%in 2000, the AI/ha declined by 42.8% and the EI/ha, based on EIQ and amount of AI for the herbicide, declined by 36.8% (14).

A more global analysis of impacts of GE crops using EIQ was performed in 2006, comparing typical EIQ values for conventional and GE crops and aggregating these values to a national level (15). Assumptions were made to perform these calculations; e.g., pesticide use levels were based on typical herbicide and pesticide treatment regimes for conventional and GE crops provided by extension and research advisors in particular regions (16). Given the caveats of the assumptions, the conclusion was that GE crops resulted in significant reductions in the global EI of production agriculture (table 5 in Reference 15); e.g., since 1996 the overall EI associated with pesticide use on HT soybean, corn, cotton, canola, and Bt cotton decreased by 15.3%.

In 2002, under supervision of the International Union for Pure and Applied Chemistry, an international team from various fields of crop protection chemistry undertook a fiveyear project to analyze pesticide use in GE versus conventional crops and to estimate changes in EI (1). They used data from public sources, including the scientific literature and reports published by various institutions. In contrast to several studies prior to 2002 that focused on AI quantities and economic effects of GE crop adoption, this study estimated the EI of changes in pesticide usage (5) using 2004 data collected by NCFAP (2) on herbicide usage on GE and conventional crops in the United States. For HT canola, cotton, maize, and soybean, total quantities of herbicide AI used in general decreased from 25 to 30% compared with conventional varieties; reductions in total EI of herbicides used were also observed with GE versus conventional crops (table 1 in Reference 5). Reductions were also observed for total EI per hectare (39 to 59% reduction) and for impacts on farm workers (40 to 68% reduction), consumers (35 to 59% reduction), and ecology (39 to 55% reduction). The numbers are generalizations based on the data used and could vary among locations. Notably these results are comparable to another study (17) in which a pesticide use footprint was calculated; this study showed that the positive effects of utilizing GE varieties were greater based on EI per unit area than on AI quantities.

When looking at herbicide usage and EI, it is important to note that in addition to use on GE crops, herbicides can be applied directly to conventional crops. Also, depending on weed pressure, multiple applications can be used in the same area during the same season. Taking these facts into consideration, glyphosate use per acre has increased dramatically from 1995 to 2005, coupled with a concomitant dramatic drop in the use of other herbicides (figure 3 in Reference 5). Cultivation of GE HT crops has also had other positive effects on the environment, i.e., increases in low- or no-till practices and use in combination with integrated pest management schemes (18), which were made possible because early season pesticide sprays could be eliminated, allowing beneficial insects to establish.

Most nonanecdotal analyses on AI usage and EIQ focus on North America, mainly because most GE HT crop acreage is in this region. Recently, an analysis of the potential EI of introducing HT crops into the European Union agricultural system was undertaken (19), despite the fact that acreage of GE crops currently in the European Union is limited. Using large-scale experimental data for HT sugar and fodder beets and to a lesser extent HT canola, it was concluded that amounts of herbicides used on HT beets were reduced, whereas those on HT soybean versus conventional were slightly higher; the latter observation is comparable to the situation in the United States. Besides North America and the European Union, other countries (e.g., Argentina, China, India, and South Africa) grow large acreages of HT and Bt varieties and pesticide usage has been studied. Most reports indicate pesticide use and cost decrease following adoption of Bt varieties (table 2 in Reference 5). In Argentina, numbers of herbicide applications increased with HT soybean but use shifted to more environmentally friendly herbicides (20).

In summary, numerous studies have been conducted on pesticide usage that analyzed different data sets and methods, sometimes leading to conflicting conclusions. Some studies showed pesticide use, expressed as AI per unit area, decreased with introduction of GE HT and Bt crops; some studies showed increases. More recently, studies have focused on EI and these have shown reductions in EI, including on farm workers, consumers, and ecology. Nonetheless, additional effort is necessary to further reduce EI of agricultural production. This goal can be achieved by using the best methods and tools available, including integrated pest management, biocontrol, organic production methods, and GE organisms (see “Can Use of Genetically Engineered Crops or Organic Farming Lead to More Sustainable Agricultural Production Systems?”) to reduce EI while achieving adequate production levels.

References:

1. Kleter GA, Bhula R, Bodnaruk K, Carazo E, Felsot AS, et al. 2008.Trends in pesticide use on transgenic versus conventional crops. Inf. Syst. Biotechnol. Aug. 2008:5–7

2. Sankula S, Marmon G, Blumenthal E. 2005. Biotechnology-Derived Crops Planted in 2004—Impacts on US Agriculture. Natl. Cent. Food Agric. Policy. http://www.whybiotech.com/resources/tps/BiotechnologyDerivedCropsPlantedin2004.pdf. Last accessed 2011-12-9. PDF

3. Fernandez-Cornejo J, Caswell M. 2006. The first decade of genetically engineered crops in the United States. USDA Econ. Res. Serv., Econ. Inf. Bull. No. 11. http://www.ers.usda.gov/publications/eib11/eib11.pdf. Last accessed 2011-12-9. PDF

4. Fernandez-Cornejo J, McBride WD. 2002. Adoption of bioengineered crops. USDA Econ. Res. Serv., Agric. Econ. Rep. No. 810. http://www.ers.usda.gov/publications/aer810/. Last accessed 2011-12-9. PDF

5. Kleter GA, Bhula R, Bodnaruk K, Carazo E, Felsot AS, et al. 2007. Altered pesticide use on transgenic crops and the associated general impact from an environmental perspective. Pest Manag. Sci. 63:1107–15

6. Carpenter J, Felsot A, Goode T, Hammig M, Onstad D, Sankula S. 2002. Comparative environmental impacts of biotechnology-derived and traditional soybean, corn, and cotton crops. Counc. Agric. Sci. Technol. (CAST) June:1–189

7. Benbrook CM. 2004. Impacts of genetically engineered crops on pesticide use in the U.S.: The first nine years. BioTech. InfoNet Tech. Pap. 7. http://www.biotech-info.net/Full version first nine.pdf. Last accessed 2011-12-9. PDF

8. Vaughn T, Cavato T, Brar G, Coombe T, DeGooyer T, et al. 2005. A method of controlling corn rootworm feeding using a Bacillus thuringiensis protein expressed in transgenic maize. Crop Sci. 45:931–38

9. Mitchell P, Alston J, Hyde J, Marra M. 2003. Benefits from transgenic maize resistant to corn rootworm. ISB News Rep. Oct.:8–9

10. DiFonzo C. 2002. Status of transgenic rootworm-protected corn. Field Crop Advisory Team Alert 17 (No. 2)

11. Kovach JA, Petzoldt C, Degni J, Tette J. 1992. A method to measure the environmental impact of pesticides. N.Y. Food Life Sci. Bull. 139. NYS Agric. Exp. Stn., Cornell Univ., Geneva, NY. http://www.nysipm.cornell.edu/publications/eiq/default.asp. Last accessed 2011-12-9. PDF
Presents a method, termed the environmental impact quotient, to calculate the environmental impact of pesticides used in commercial agriculture to facilitate comparison of different pesticides and pest management practices.

12. Kovach JA, Petzoldt C, Degni J, Tette J. 2003. Method to measure environmental impacts of pesticides. NY State Integr. Pest Manag. Manual. http://fls.cals.cornell.edu/OCRPDF/139.pdf. Last accessed 2011-11-26. PDF

13. Knox OGG, Constable GA, Pyke G, Gupta VVSR. 2006. Environmental impact of conventional and Bt insecticidal cotton expressing one and two Cry genes in Australia. Aust. J. Agric. Res. 57:501–9

14. Brimner TA, Gallivan GJ, Stephenson GR. 2004. Influence of herbicide-resistant canola on the environmental impact of weed management. Pest Manag. Sci. 61:47–53

15. Brookes G, Barfoot P. 2006. Global impact of biotech crops: Socio-economic and environmental effects in the first ten years. AgBioForum 9:139–51

16. Sankula S, Blumenthal E. 2004. Impacts on US Agriculture of Biotechnology-Derived Crops Planted in 2003—An Update of Eleven Case Studies. Natl. Cent. Food Agric. Policy. http://croplife.intraspin.com/Biotech/papers/80%202004finalreport.pdf. Last accessed 2011-12-9. PDF

17. Brookes G, Barfoot P. 2005. GM crops: The global economic and environmental impact—the first nine years 1996–2004. AgBioForum 8:187–96

18. Ellsworth PC, Jones JS. 2001. Cotton IPM in Arizona: A Decade of Research, Implementation and Education, ed. J Silvertooth, pp. 199–214. Tucson: Univ. Ariz., Coll. Agric. Life Sci.

19. Kleter GA, Harris C, Stephenson G, Unsworth J. 2008. Comparison of herbicide regimes and the associated potential environmental effects of glyphosate-resistant crops vs. what they replace in Europe. Pest Manag. Sci. 64:479–88

20.  Qaim M, Traxler G. 2005. Roundup Ready soybeans in Argentina: farm level and aggregate welfare effects. Agric. Econ. 43:73–86

 

Updated 2/16/12