Even more widespread than Bt corn are herbicide-tolerant crops that survive spraying of glyphosate, the weed killer known as Roundup. (Fittingly, these crops are called Roundup Ready.) Companies that manufacture Roundup Ready corn, cotton, canola, and soybeans claim these crops are the solution to the world’s food problems, insisting that the GMO versions have higher yields, benefit farmers and the environment, and reduce herbicide use.

Anti-GMO activists disagree. “When [Roundup Ready] technology first came onto the market in 1996, most farmers had excellent weed control with only one herbicide application per crop,” says Chuck Benbrook, a research professor at
Washington State University who studies genetically engineered crops. “By 2000, the first Roundup-tolerant weeds started to emerge in fields and were surviving a low application rate.” Fighting these progressively more resilient weeds is a snowballing struggle because farmers must incrementally increase herbicide use. Whereas earlier farmers were forced to minimize glyphosate applications because it would kill their crops, Roundup plants are not affected by the chemicals. Since farmers adopted GMOs, they have increased herbicide use by 404 million pounds—a 7 percent jump.

This worries Benbrook. “The sheer volume of glyphosate has led to soil changes that reduce a plant’s ability to draw up various mineral micronutrients [like zinc, chromium, and manganese],” he says. This also renders plants vulnerable to bacterial and fungal attacks. The downsides? Lower crop yields, less nutrition, and more fungicide spraying.

Plus, a whole host of negative effects result from massive Roundup use. Most recently, a study published in the scientific journal Entropy suggests that long-term exposure to glyphosate residues could be linked to a suite of nasty human-health issues, including gastrointestinal disorders, Alzheimer’s, and certain cancers. As weeds continue to become even more resistant, the biotech industry’s strategic answer is to breed seed resistance to more precarious herbicides, including 2,4-D, an ingredient in Agent Orange. Frighteningly, these higher-risk chemicals have a habit of drifting to neighboring crops, which can be particularly devastating to flowering vegetable and fruit crops, says Benbrook.