Superweeds and Superpests

The use of genetically modified crops was intended to reduce the need for herbicides to control weeds and insecticides to control pest insects. However, The New York Times reports that instead herbicide use increased over 16 years, while insecticide use decreased somewhat. The widespread use of a single herbicide glyphosate, sold under Monsanto’s brand name Roundup, has resulted in the evolution of a number of glyphosate-resistant weeds. The Times piece, http://green.blogs.nytimes.com/2012/10/05/the-legacy-of-pesticides-superweeds-and-superpests/?src=rechp, describes different approaches to the use of these genetically modified organisms. “Roundup Ready” corn, soybeans, and cotton seeds were planted on 1.37 billion acres from 1996 to 2011. The GMO plants, tolerant of the herbicide glyphosate, were supposed to reduce or eliminate the need to till fields and reduce the need for harsher chemicals. The use of these GMOs was supposed to also save money and be less stressful on the environment. As glyphosate-resistant weeds increased, increases in the use of glyphosate slowed; and in 2010 the National Research Council warned that, “Eventually, repeated use will render glyphosate ineffective.”

Those deploying the genetically modified seed containing the Bt gene producing toxins from the soil bacterium Bacillus thuringiensis recognized the potential for evolving resistant insects, and they took precautions. They required that a percentage of non-Bt seed be planted with Bt crops to ensure that some insects susceptible to the Bt toxin survive to mate with survivors of the Bt crops. Otherwise, surviving pest insect populations could become increasingly resistant to the Bt toxin with each generation. The mechanism for ecological harm from chemical pesticides was described by Rachel Carson in Silent Spring 50 years ago: “First, many of these chemicals are indiscriminate, killing not only pest but also the predators and parasites that help to keep them at bay. Second, surviving pest populations become increasingly resistant to the applied toxins with each generation, as those most susceptible to the toxins die off. It’s natural selection in overdrive.” Today’s photo: applying herbicide to control grasses in GMO soybeans.

--Richard