Introduction by Chuck Foresman, Weed Resistance Brand Manager, Syngenta Crop Protection

How much are we pushing our limits when it comes to glyphosate resistance? With its continual and growing use in glyphosate-tolerant cropping systems, the amount of acres treated with this single herbicide represents an overwhelming percentage of farmland acres across the U.S. And, it is increasing at a much faster rate than any other technological innovation in agriculture. Even in the event a new herbicide with a different mode of action was discovered today to help alleviate resistance pressure, it would take at least 10 years for it to become available to the market.

Dr. Stephen Powles, a professor at the University of Western Australia and an expert on herbicide resistance, has his own views on how this will affect American farmers. In the attached paper, Dr. Powles provides his perspective on why he believes it is so important to preserve this technology on the most productive cropland in the world.

As weeds, such as Palmer pigweed, make headlines for resistance to glyphosate, 10 years is too long to wait for a solution. Today, knowledge and proper management practices are our best weapons. And as Dr. Powles points out, glyphosate and glyphosate-tolerant crops are superior to any other system of weed control and are too good to lose. With pigweed, marestail and common ragweed already confirmed and many other weeds under scrutiny, it leaves the question lingering – what’s next?

The coming plague: Glyphosate resistant weeds in American croplands

Professor Stephen Powles, Director of the Western Australian Herbicide Resistance Initiative (WAHRI)  since 1998, has had a lengthy career in the plant sciences in NSW, South Australia and ACT as well as periods in the USA, UK and France. He is an international authority on all aspects of herbicide resistance from basic biochemical understanding of how plants develop resistance, through to practical management on-farm. He is equally interested in both the generation of new knowledge and its application in cropping systems.

Stephen B. Powles, PhD
Professor & Director- Herbicide Resistance Initiative
University of Western Australia
Australia

The past decade has brought a revolution in American agriculture.  The technological innovation of genetically modified soybean, cotton, canola and corn engineered to be resistant to the herbicide glyphosate (Roundup Ready^® crops), has brought many advantages to U.S. farmers.  Glyphosate tolerant technology enables crops to be unaffected by glyphosate, whereas this effective, environmentally benign herbicide controls a wide range of infesting, yield-robbing weeds, resulting in cleaner crops and higher yields. With this system, glyphosate is superior to any other system of weed control, and has environmental benefits such as reducing destructive soil cultivation.  Consequently, glyphosate tolerant crops are widely planted by American grain producers.  Indeed, this embrace by American grain producers of glyphosate tolerant soybeans and cotton is the fastest adoption of an agricultural innovation ever.   Currently, 90 percent of all soybean and cotton and 30 percent of the corn acres in America are glyphosate tolerant.  As corn and soybeans are grown in rotation in the same fields across vast areas (and with cotton in the South) this means that huge areas of America’s croplands are annually treated with glyphosate. 

Life-saving antibiotics and crop-aiding herbicides such as glyphosate are major contributors to the vibrant health and abundant food available to many people in many parts of the world.  However, lamentably, they are often treated just as cheap commodities that will always be there to provide efficacious and rapid control of unwanted infections, pests, etc.  However, the reality is that over-reliance results in the evolution of resistant populations and the potential loss of these precious resources for future harvests and future generations.  Antibiotic resistance is a looming threat to continued human health and pest resistance to agrochemicals threatens food production.  With the huge reliance on glyphosate for weed control in America, resistance is a threat to American crop production and therefore world food supplies.  

The massive adoption of glyphosate tolerant crops means that there is excessive reliance on glyphosate to control crop weeds across much of America’s croplands.  While glyphosate means a quick death for billions of yield-robbing weeds its almost exclusive use across vast areas also represents a very strong selection pressure for any weeds carrying genes endowing resistance to glyphosate.  Currently, each year some 180 million acres of prime American cropland is being treated with glyphosate.  This is an unprecedented usage of a single chemical.  Never before in history has the same chemical been applied persistently for pest control across such a vast area.  Such massive reliance on one chemical tool in this way carries with it the potential for its own destruction.  Ever since Charles Darwin we have known that nature ensures survival due to genetic variation evident in very large populations.  Persistent and widespread glyphosate treatment of billions of wild, weed plants in America is inexorably selecting for weeds able to resist glyphosate and therefore to thrive when all their competitors around them have succumbed.  This is exactly what is now underway across American croplands.  Weeds that are resistant to glyphosate first appeared in Australia but are now coming to prominence in American croplands so dominated by glyphosate.  Glyphosate resistant marestail (horseweed or Conyza canadensis) now infests at nearly five million acres of American crop fields.  This weed produces many small, light seeds equipped with a tiny parachute enabling them to float huge distances on the wind.  As over 180 million acres of America’s croplands are glyphosate tolerant, resistant marestail will soon be everywhere.  Even more worrisome for American agriculture is that currently isolated glyphosate resistant populations of really economically damaging weeds are now known in American croplands.  Glyphosate resistant populations of lambsquarters (Chenopodium album), palmer amaranth (Amaranthus powelli) and ragweed (Ambrosia  xx) are known in glyphosate tolerant crop fields in a number of U.S. farm states. 

I believe that there is massive over-reliance on glyphosate in American croplands and that the productivity of American corn and soybean is at risk due to the looming threat of glyphosate resistant weeds.  While the package of glyphosate and glyphosate tolerant soybeans, corn and cotton delivers great value and productivity to American agriculture, this tremendous technological innovation is now at risk.  There is simply a massive over-reliance on glyphosate, which must inexorably lead to the evolution of glyphosate resistant weeds.  If U.S. cropping persists with glyphosate as it currently does then there will be the widespread development of glyphosate resistant weeds across large areas of U.S. croplands. 

We must recognize the biological reality that glyphosate resistant weeds will evolve if we let them.  We must recognize that glyphosate is a precious resource that should be conserved for future generations and future harvests.  We should recognize that there is massive over-reliance on glyphosate in much of American agriculture.  We should try to prevent glyphosate resistant weeds developing across some of the most productive croplands in the world.  Only by reducing our dependence on glyphosate will we have a chance of minimizing the rate of glyphosate resistance and therefore saving this precious resource for future generations and future harvests.  The fact is that glyphosate and glyphosate tolerant crops are too good to lose.  Only by recognizing their value and the danger that their overuse poses will there be a chance of conserving them for future years.  The time to act is now!