The corn shoppers find on supermarket aisles and at farm stands is called “sweet corn” because it contains more sugar than its ancestor, field corn. People eat sweet corn fresh on or off the cob, frozen or canned.
Some 28,000 American farmers grew 3.1 billion pounds of sweet corn in 2012, according to the U.S. Department of Agriculture, generating a market valued at $822 million in 2012 (USDA 2012a). But this special type of corn, a natural mutation that is believed to have emerged in Pennsylvania in the mid-18th century, represents less than 1 percent of American corn production (Iowa State University 2011).
Most of the American corn crop is “field corn,” a starchy grain highly valued worldwide for its versatility. This year, American farmers are projected to produce about 14 billion bushels of corn, or 980 billion pounds, according to the USDA, vastly more than any other grain (USDA 2014).
Corn is a component of a wide variety of goods on the American marketplace. The USDA estimates that 40 percent of the U.S. corn crop is processed into ethanol for use as engine fuel, 37 percent goes for livestock feed and 11 percent is made into processed food ingredients like corn flour, corn syrup, corn starch and cooking oil (USDA 2012a). As of 2011, cornfields covered 92 million acres in all 50 states, with the most intense concentration in the Midwest.
Today’s cornfields are particularly vulnerable to pest infestations because corn is typically grown in huge monocultures, with little or no crop rotation. Historically, farmers rotated crops to disrupt the life cycle of insects and diseases (Altieri 2000). They diversified their crops. Modern farmers often resort to chemical herbicides, insecticides and fungicides.
Based on figures from the USDA and U.S. Environmental Protection Agency, EWG calculates that every year, American farmers apply around 300 million pounds of the active ingredients in pesticides to their cornfields (USDA 2012b).
Because the thick husk protects corn kernels from pesticide applications, few pesticides show up as contaminants on kernels that would be eaten by people and animals. In USDA tests in 2008, 2009 and 2010, neither fresh nor frozen sweet corn tested positive for significant numbers of pesticide residues (USDA2009, 2011b, 2012c). In 2010, USDA scientists found no pesticides at all on 99 percent of sweet corn samples (USDA 2012c). They tested field corn in 2007 and 2008 and found minimal pesticide residues (USDA 2009, 2010).
Even though pesticides don’t show up in your frozen corn or corn on the cob, they can still present serious threats to people and other living things. The most common pesticide used on corn is Monsanto’s Roundup, whose chemical name is glyphosate. American farmers used on Roundup on two-thirds of U.S. corn acres in 2010, according to the USDA (USDA 2011c). Scientists have determined that glyphosate harms soil microbial communities, aquatic organisms, beneficial insects, birds and mammals (Benbrook 2012, FOE 2001). The U.S. Geological Service detected glyphosate in more than one third of water samples from 51 Midwestern streams and found a chemical generated when glyphosate broke in more than two-thirds of those samples (USGS 2003). Glyphosate has a relatively low oral and dermal toxicity. There is some concern that high doses may cause birth defects in mammals and other developmental problems (Paganelli 2010).
Conventionally-grown corn seeds are commonly treated with neonicotinoid insecticides that may significantly threaten bees. The Canadian government blamed neonicotinoid-treated corn seeds for an unusually high number of honeybee deaths in Canadian corn country corn in 2012 (Health Canada 2013). Last year, the European Commission restricted three neonicotinoid pesticides for two years after the European Food Safety Authority called them "high acute risks" for bees (EU 2013).
Some 90 percent of the American field corn crop is genetically engineered to resist herbicides or to produce a protein derived from bacillus thringiensis bacteria that can kill certain insect pests such as the southwestern corn borer (USDA 2013). Consequently, corn-based sweeteners, starches and oils in processed foods are almost certainly manufactured from genetically engineered corn. In contrast only a small amount of GE sweet corn can be found on the U.S. market. Most sweet corn has not been genetically engineered.
Scientists have not thoroughly explored the implications of genetically modified corn for human health and for the environment, particularly over the long term. EWG advocates more safety research and labeling of GE foods, on grounds that consumers have the right to know what is in their food. In the meantime, those who want to avoid GE corn products and other GE ingredients should check EWG’s Shopper’s Guide To Avoiding GE Foods.
The rapid adoption of GE field corn varieties has led to an unintended and unwanted side effect: data show that the volume of herbicides applied to corn varieties genetically modified to withstand herbicide treatments has increased (Benbrook 2012). The reason: some weeds have mutated to resist herbicides. These so-called superweeds are studier and harder to kill than weeds in their natural state and require heavier applications of weed-killer (Farm Industry News 2013). Agribusiness has responded by turning to stronger, more toxic herbicides and new GE corn and soy varieties.
One type of genetically modified corn called “Bt corn” contains insect-killing bacteria in its internal structure. Planting Bt corn seem to reduce pesticide use for a while. However, the pests that Bt corn was created to kill have been developing resistance to the Bt toxin, forcing famers to fall back on chemical insecticides (Thompson 2013).
Altieri M. 2000. Modern Agriculture: Ecological impacts and the possibilities for truly sustainable farming. http://nature.berkeley.edu/~miguel-alt/modern_agriculture.html
Benbrook C. 2012. Impacts of genetically engineered crops on pesticide use in the U.S. – the first sixteen years. Environmental Sciences Europe. 24:24.
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Thompson 2013. Chemical creep: Farmers return to pesticides as GMO corn loses bug resistance. http://grist.org/news/chemical-creep-farmers-return-to-pesticides-as-gm…
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USDA. 2011c. Agricultural Chemical Use: Corn, Upland Cotton and Fall Potatoes 2010. U.S. Department of Agriculture. http://www.nass.usda.gov/Surveys/Guide_to_NASS_Surveys/Chemical_Use/Fie…
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