Get ready for a new controversy. Corn and soybeans that are genetically engineered to resist the weed killer 2,4-D are heading for approval. And they are also heading for an onslaught of opposition from activists and some farmers. The idea of genetic modification for herbicide resistance is not new. Corn, soybean, canola and cotton growers in North America have been using Monsanto’s “Roundup Ready” seeds for years. Previous to the introduction of this technology large amounts of chemicals had to be applied to plowed fields before seeding to eliminate weeds. With Roundup Ready crops there is less need for plowing, reducing soil erosion. After seeds are planted, application of glyphosate, the chemical name for Roundup, wipes out the weeds. Furthermore glyphosate has a better toxicological profile than most other herbicides.
But a problem has emerged, one that was actually foreseen. Some weeds have become resistant to glyphosate. This is not a consequence of genetic modification, it is a consequence of biology. Plants will eventually develop a resistance to any herbicide or pesticide. In the southern US, pigweed (Palmer amaranth) has developed resistance to glyphosate and farmers now have to resort to the expensive process of hiring workers to pull out this weed that is overrunning cotton fields by hand. The answer to the problem, farmers hope, lies in Dow Chemical’s 2,4-D resistant cotton. Dow’s new fangled seeds contain a gene from a soil bacterium that codes for a protein that decomposes 2,4-D into harmless chemicals. Basically, the idea is to replace crops that have become resistant to glyphosate by crops that are resistant to 2,4-D. This is a similar game to the one that we are forced to play with antibiotics. When microbes become resistant one, as they always will, we have to look for an alternate substance.
In this case, the issue, at least in some eyes, is that 2,4-D is not as safe as glyphosate. It is also saddled with the curse of having been one of the components in “Agent Orange,” the infamous defoliating agent used during the Viet Nam war. It is true that 2,4-D was part of Agent Orange, but the health problems attributed to Agent Orange were caused by the notorious tetrachlorodibenzodioxin (TCDD), a contaminant in 2,4,5-T, the other component of Agent Orange. 2,4-D has actually long been used by farmers, as well as by the lawn care industry, to control weeds, albeit not without controversy. Some have suggested a link to lymphoma and endocrine disruption but numerous investigation by various regulatory agencies have failed to support this. Recently the Environmental Protection Agency rejected a petition from the Natural Resources Defense Council to remove 2,4-D from the market on health and safety grounds.
Still, people worry that the introduction of 2,4-D resistant seeds is going to dramatically increase the use of the chemical. There is also concern that 2,4-D has a greater drift potential than glyphosate. So a farmer growing crops that are not resistant to 2,4-D may see his yield decrease if there is drift from a neighbouring farm. Dow Chemical contends it has developed technology to reduce drift. But no matter what safe guards are introduced, there will be opposition, much of it emotional. People don’t want what they are labeling as “Agent Orange crops” and are expressing their opinion through petitions. They will likely also oppose Monsanto’s new soybeans, corn and cotton that are resistant to the herbicide dicamba. Of course they will oppose anything that is introduced by Monsanto.
