The resistance to resistance: What is a weed?

By Dennis Keeney

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.

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