Science & Our Food Commentary Series

By Marcus Glassman, Research Associate, Global Agriculture & Food

Many on either side of the genetic engineering (GE) debate cite the relationship between GE crops and pesticides as one of the greatest consequences of GE crops’ environmental impact. According to GE proponents, the advent of GE crops has allowed farmers to radically reduce their pesticide use; use fewer and less harmful chemicals; and promote conservation-minded agriculture practices. Opponents say quite the opposite: That GE crops have ushered in an era where farming uses far more pesticide chemicals than ever before, with a larger, more negative impact on the environment. Both sides are right. And, both sides are wrong.

To begin, “pesticide” is something of a misnomer: What we are really talking about are insecticides, that kill insects, and herbicides, that kill weeds. Generally, insects and weeds are controlled through chemicals, but genetic engineering has taken things one step further with GE insecticide-resistant crops and GE herbicide-resistant crops. GE insect-resistant crops produce their own insecticides, which repel and kill-off insects that  prey on the plants, while GE herbicide-resistant crops are resistant to herbicides, the chemicals that are sprayed to kill weeds—a “weed,” in this context, being all plants in a field that weren’t planted by the farmer.

From an environmental perspective, insect-resistant GE crops have been a success story. The most common insect-resistant GE crops are those engineered with a gene from Bacillus thuringiensis, or Bt, a bacteria that produces a protein that is toxic to a narrow range of insects—chiefly beetles and caterpillars—but otherwise harmless to other insects, animals, and the environment. Bt corn and Bt cotton are commonly grown in the US, and significantly reduce the amount of chemical insecticide needed by farmers. When farmers do spray, they can do so with more precision and less impact on the environment; fewer broad-spectrum insecticides are needed, which means fewer beneficial and non-pest insects are killed; and when used as part of an integrated pest management system, Bt crops can help to reduce on-farm insecticide use by up to 80 percent.   

Unfortunately, it’s not a perfect system.  As critics of GE will readily—and correctly—point out, where Bt crops are widely planted, insect populations can quickly develop Bt resistance. As the number of resistant insects grows, the insecticidal properties of GE Bt crops lose their effectiveness, forcing farmers to spray increasing volumes of insecticides. Entomologists estimate that Bt resistance can be avoided by planting a ratio of 50:50 Bt and non-Bt crops on a farm. But, farming is a business, and Bt crops require fewer chemicals and produce higher yields than non-Bt crops, and are therefore more profitable. Due to this economic pressure, the ratio of Bt to non-Bt crops planted in reality trends closer to 95:5—and resistance ensues.

Herbicide-resistant GE crops have been more of a mixed story from an environmental perspective. These crops are enormously popular in the US: 83 percent of corn and 93 percent of soy were herbicide resistant—totaling 155 million acres—in the US in 2013. Far and away the most popular of the herbicide-resistant crops are the Roundup Ready crop lines produced by Monsanto. These crops are resistant to the chemical glyphosate, the active ingredient in the Monsanto-produced herbicide Roundup, a popular spray that kills most all plants—including crops that aren’t genetically engineered to be resistant to the chemical. 

Prior to the development of Roundup Ready crops, glyphosate was sprayed on fields before crop plantings and after crop harvests to kill off residual weeds, but couldn’t be used during the growing season. With the creation of glyphosate-resistant GE crops, however, suddenly farmers could spray glyphosate directly on crops to control weeds: Doing so was quicker, cheaper, and more effective than alternative methods of weed control. It allowed farmers to switch from more toxic herbicides, like metolachlor (a known groundwater contaminant), to glyphosate, which, although not entirely harmless, breaks down quickly in the environment and has comparatively low toxicity. And, it allowed farmers to reduce the acreage tilled for planting—a tremendous boon for soil conservation.

The major issue with using so much glyphosate? Glyphosate-resistant weeds. What was once a chemical only used sparingly has become a chemical for everyday use. And whereas a variety of herbicides were previously used on farms, glyphosate-resistant crops are only resistant to glyphosate—so that’s the one chemical farmers use most. Using a single chemical, months at a time, on what amounts to well over 80 percent of the US cropland, creates strong environmental pressure for weeds to adapt. Any weed that can survive in such a glyphosate-saturated environment has practically no weeds to compete against for water or space, and can therefore flourish and spread—not unlike the issue faced by Bt crops with Bt-resistant insects.

The development of GE pest control strategies has fundamentally transformed agriculture’s relationship with the environment. At its best, GE technology has reduced the amount of chemical insecticides used on farms; glyphosate has reduced the total toxicity employed for weed control; and herbicide resistant crops in general have made soil conservation practices easier than ever to implement. But the reality is not so perfect: Marketing strategies by biotech firms, economic pressures to improve farm efficiencies, and a lack of governmental oversight have undercut the ethos of preservation of the commons needed to ensure these products remain useful. Increasing rates of Bt-resistant insects and glyphosate-resistant weeds lead farmers to use greater volumes of more toxic chemicals to achieve wanted pest control results; worsen the state of agriculture’s environmental impact; and tarnish the public’s perception of what GE technology is and what it can do.

Although the current use of GE crops seems to be a real-time example of the tragedy of the commons, it’s important to remember that it didn’t have to be so, and doesn’t have to repeat itself. As genetic engineering technology advances, there is no reason to think that what comes next won’t be just as innovative as those products we’ve seen. The question is: Will we have learned our lesson from our mistakes in time to see the promise of those technologies, or will it be another case of history repeating?


Read additional posts in the Science & Our Food series:

• Food Security, Climate Change, and Biotechnology: A Look at Bangladesh, July 28
• The Environment and GMOs: Pesticides, Promises, and Squandered Possibilities, July 21
• Golden Rice: Solution or Symbol?, July 14
• Hawaiian Papayas and Florida Oranges: Combating Disease with Genetic Engineering, July 7
• Public Perceptions and Understanding of Genetically Modified Foods and Labeling, June 23
• Scientists and the Public Struggle to See Eye-To-Eye on Science and Technology, June 16