The GMO High-risk List: Corn

Corn is a staple food for a full third of the human population and one of the most commonly grown grains in the world. It's also prominent in many Americans' diets — but not as a nutritious staple. In the U.S., corn appears as sweeteners or additives with little nutritional value or is used in livestock feed.

Because most corn grown in the U.S. is genetically modified, the Non-GMO Project Standard considers corn a high-risk crop.

Since the first genetically modified corn was released in 1996, another 243 distinct varieties of GMO corn have been created. In 2022, GMO corn made up an estimated 93% of the corn planted in the U.S., occupying more than 86 million acres.

What are the most common types of corn? Which ones are most likely to be GMOs, and, most importantly, where might they show up at the grocery store?

Types of corn

Field corn is the most commonly grown kind of corn, making up about 99% of the corn grown in the United States. Field corn differs from the tender, sweet corn you eat off the cob during summer barbeques. It's harvested late when the kernels are dry. Field corn is also called "dent corn" because its kernels appear dented.

The vast majority of field corn isn't used to feed people. Instead, it is used for livestock feed or converted to ethanol for cars. The small amount of field corn that ends up in food for humans is processed into easily identified ingredients such as corn starch or corn syrup, or hard-to-spot derivatives such as citric acid, cellulose, maltodextrin, flavorings and some vitamins.  

Sweet corn is what most people think of when they picture corn. You can buy it in the grocery store on the cob, canned and frozen in bags. True to its name, sweet corn is harvested early when the kernels still contain a lot of moisture and sugar.

Until recently, genetically engineered sweet corn was uncommon. However, Monsanto (now owned by Bayer) introduced the first GMO sweet corn in 2011. Genetically modified sweet corn was engineered to resist weedkillers and produce its own insecticide. Sweet corn makes up comparatively little of total corn production, growing on less than a million acres of U.S. farmland. In 2018, genetically modified varieties comprised an estimated 10-25% of all U.S.-grown sweet corn. 

Flint corn is a distinct type of corn that's even harder than field corn. Flint corn has a high nutritional value, and it can be dried and used for corn meal, corn flour, polenta and grits. It makes up very little of all corn grown in North America. 

Popcorn comes from flint corn. Popcorn is not considered a high-risk crop under the Non-GMO Project Standard for two reasons: 1) No GMO popcorn is available on the market at this time, and 2) Popcorn has a natural immunity from GMO contamination. (For more on popcorn, read "Will Biotech 'POP' Organic Corn's Best Defense Against GMO Pollen?"). However, store-bought and pre-made popcorn snacks might contain other GMOs such as butter, canola oil, sugar, corn syrup, lecithin, enzymes, lactic acid and many flavorings.

GMO traits

The most common traits engineered into genetically modified corn are herbicide tolerance and insect resistance. 

Herbicide-tolerant (HT) corn is immune to weedkillers such as glyphosate, the active ingredient in Roundup. Farmers who grow HT corn can spray Roundup directly on their crops without harming the corn. HT crops have led to a 15-fold increase in herbicide use and contributed to the rise of herbicide-resistant weeds. 

Corn that is modified for insect resistance is known as "Bt corn," after the toxin Bacillus thuringiensis. Bt corn produces insecticide in every cell in the corn plant, poisoning insect pests that eat the corn. Because the insecticide is inside the cells, it can’t be washed away. 

More than 87% of corn grown in North America is genetically modified “stacked” trait varieties that carry both HT and Bt traits.

Genetically modified corn is so common that it might feel impossible to avoid, but that’s why the Non-GMO Project was created. Under the Non-GMO Project Standard, products that contain corn as a major or minor ingredient face special scrutiny, including testing, ingredient tracing or segregation.

The Non-GMO Project Butterfly helps preserve the precious 7% of corn grown in the U.S. grown from non-GMO seed. To protect and build the demand for non-GMO corn and to protect your right to choose whether or not to consume GMOs, look for the Butterfly!