The resistance to resistance: What is a weed?
The ability of natural systems to overcome assaults by outside forces that threaten their livelihood is nothing short of phenomenal. When I was kid growing up in Iowa in the 1950s, I recall when we sprayed DDT on the cows to control flies, except the flies soon fought back, so we had to use more. First used as an outgrowth of nerve gas from WWII, DDT was regarded as a lifesaver for control of mosquitoes carrying malaria but it soon became ineffective. Never mind that the full health and environmental risks of toxic DDT were never fully evaluated before it was in widespread use, and when it was found in milk, some people began to worry. Other pesticides, such as dieldrin and aldrin, were substituted, but mosquitoes again became resistant in 18 months or less.
Not to be deterred, humanity has continued to try to use pesticides to control pests over and over—only to find that pests continue to fight back over and over. Now more than 500 species of insects and fungus are resistant to pesticides and the list continues to climb.
Even corn rootworm, which used to be controlled by alternating corn with another crop such as soybeans, has figured out that it can exist nicely with the soybean and come back the next year, a phenomenon known as extended diapauses.
Aside from insects, resistance also operates efficiently in the plant world. Weeds are ever with us. Indeed they are called weeds because they end up where they are not wanted and cause economic damage. In 1943 Aldo Leopold wrote a classic essay called “What is a Weed.” The essay, published in River of the Mother of God (UW Press), said “To live in harmony with plants is, or should be, the ideal of good agriculture. To call every plant a weed which cannot be fed to livestock or people is, I fear, the actual practice of agricultural colleges. [...] The first false premise is that every wild species occasionally harmful to agriculture is by that reason of fact to be blacklisted for general persecution.”
I spent many hot days chopping weeds out of corn and soybean fields when I was a youth. When a miracle product called 2,4-D (an early Monsanto product) came along to use on the corn fields, I rejoiced. But lo and behold, by 1957, weeds were reported in Hawaii sugarcane fields that were resistant to 2,4-D. Weed scientists did not worry much. The slow growth pattern of weeds meant it would take many years before widespread resistance would occur. But weeds did not wait.
The triazines, especially atrazine, came into widespread use the 1960s. Predictably, weed resistance soon developed. While triazine resistance is commonplace, atrazine remains a major herbicide for corn.
But all was not lost. In the 1970s a Monsanto organic chemist named John Franz found a triamine salt, called glyphosate, that had broad spectrum toxicity toward green plants. Glyphosate was branded as Roundup and formulations were first marketed in 1976. Over the last three decades, glyphosate has brought enormous profits to Monsanto, which had exclusive U.S. rights until 2000 when the patent expired. Roundup has been the most widely sold herbicide worldwide since 1980.
The company’s profits greatly expanded with the introduction of crops genetically engineered to be tolerant of Roundup. With the introduction of Roundup Ready (RR) crops patented by Monsanto, the company's sales not only of the chemical but also of the seed and associated patents skyrocketed.
Over 90 percent of soy, 75 percent of cotton and 70 percent of corn grown in the U.S. in 2009 contains the RR trait. This amounts to 130 million acres of corn and soy, according to the U.S. Department of Agriculture.
While Roundup has been touted as safe and environmentally friendly, much data indicates the contrary. Of particular concern are the “inert” adjuvants (chemicals added to enhance the activity of the pesticide) that often are not disclosed nor tested by EPA.
Worldwide, at least 25 countries have now adopted biotech crops (statistics are not available to sort these out by herbicide-tolerant and insecticide-tolerant crops)—amounting to a total of over 300 million acres.
But as predicted by weed and ecological scientists for a couple of decades, resistance to Roundup is developing, and the number of new species resistant to Roundup has increased markedly in the last few years. Many of the resistant weeds are economically important and difficult to control. Some, such as waterhemp, have been observed to have developed resistance (PDF) to at least three different classes of herbicides.
Over 19 genotypes are Roundup resistant worldwide. And with the increasing potential for large acreages of Roundup-ready alfalfa and sugarbeet crops, more difficult to control weeds will likely emerge. Importantly for all herbicides evaluated by 2009, the Weed Science Society lists 346 Resistant Biotypes, 194 Species (114 dicots and 80 monocots) and over 340,000 fields worldwide that have developed resistance. This covers virtually all herbicides that have been used commercially since the chemical era began.
Growing resistance to herbicides means farmers have to use more to achieve the same effect. The amount of herbicide used in U.S. agriculture has increased dramatically—up 46 percent in the last 13 years for corn, cotton and soybean production. Much of this increase is attributed to Roundup resistance. Remarkably, the Associated Press reported earlier this week that Monsanto was paying cotton farmers an additional $12 an acre to cover the costs of other herbicides to use alongside of Roundup. Further, the use of older, more toxic herbicides such as 2,4-D and paraquat are increasing, adding to water quality and offsite drift issues, and another gallery of resistant weeds.
Where this will lead is obvious; curtail herbicide use or face the consequences of less herbicide effectiveness with more economic, human health and ecological consequences. I would bet that if they could, Aldo Leopold and Charles Darwin would have a good laugh at this conundrum.
Chemical-based weed control may be hitting a brick wall—or at least a wall that is getting more difficult to traverse. No major new pesticides are being developed for corn or soybeans. The last major advancement in chemical weed control was pigment inhibitors (chemicals that prevent plants from forming photosynthetic pigments) developed in the 1980s. We are entering a new era where farmers cannot rely on technology to bail them out.
This little horror story points out once again the fallacies of industrial agriculture, built on short-sighted corporate control of crop inputs, and supportive government policies. Weed scientists sounded the alarm on resistance years ago but many were told to cool it for fear of angering the corporate sponsors of University research and outreach funding. Of course, the discipline of weed science likes to take credit now for being right, but where were they when they should have spoken out more strongly?
When I was executive director of the Leopold Center at Iowa State University in the 1990s I banned research funding for biotech crops, and was widely criticized for this move. Other leaders such as Dr. Chuck Benbrook who previously led the National Academy of Sciences Agriculture Committee spoke out, and soon lost their jobs. The pattern is a familiar one for academia, except the stakes for the future of agriculture are becoming more and more serious. It is up to groups such as IATP to move the playing field back to biointensive pest control (the use of ecological principles to control pests, rather than relying solely on pesticides).
In a future blog, I will tackle the more evasive issue raised by genetically engineered crops containing the Bacillus thuringiensis (Bt) gene for control of moths and borers. Stay tuned.
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