Note: DuPont scientists conducted a review of current scientific literature related to the impact of biotechnology on crops and weed management. This information will be updated from time-to-time. We welcome new scientific information, encourage you to read about these areas and share your perspective

1. Introduction
2. Developing New Herbicides and Herbicide Resistant Crops
3. Herbicides, Herbicide Resistant Crops and DuPont Product Development
4. The Impact of Herbicide Resistant Biotech Crops
5. Future Steps

Growers must control weeds that compete with their crops for water, nutrients and sunlight. Depending on the crop and its location, weeds can decrease crop yields from 35% - 100%. A number of options for minimizing the impact of weeds on crop productivity are available to growers; one option is application of herbicides to the weeds.

Virtually all crops have some degree of innate resistance to some herbicides but not others. In the 1940's, crop developers began exploiting this selective resistance to control weeds in cornfields. Within a decade, over 50% of the U.S. corn acreage was planted to varieties that could survive exposure to certain herbicides. By 1975, more than 80% of the corn and soybeans grown in the U.S. were herbicide resistant varieties; that figure is now well over 95%. Today growers all over the world minimize the negative impact of weeds by using herbicides and herbicide resistant varieties of most crops, including all of the major commodity crops, as well as small acreage horticultural crops, such as vegetables.

An ancillary benefit of herbicides is the impact their use has on soil erosion. Herbicides and herbicide resistant crops allow growers to use minimal tillage or no-till techniques, which significantly decreases the impact of agriculture on soil erosion. Additional information about the topic of conservation tillage and plant biotechnology is available on the Conservation Technology Information Center website. [.pdf]

Weeds, like all crop pest, respond to any control tactic by evolving biological mechanisms to resist control.  » More

The first documented case of a weed becoming newly resistant to an herbicide occurred in the late 1960's. By 1980, scores of weeds species contained some populations that had evolved resistance to at least one herbicide that had been used to control it. Today more than 290 types of herbicide resistant weeds are present in agricultural fields around the world. (Data from the international survey of herbicide resistant weeds can be found at WeedScience.com website.

To maintain the effectiveness of the fundamental weed control strategy of using herbicides with herbicide resistant crop varieties, growers must continually have access to new options. Scientists use two research approaches to increase the number of options for pairing herbicides and herbicide resistant crop varieties: discover and develop new herbicides or broaden the genetic capacity of a crop to resist herbicides that are already on the market.  » More

Discovering new herbicidal compounds was the preferred approach in the 1950s-1970s. Newly synthesized molecules were sprayed on weeds; those that controlled weeds were then tested to see which crops, if any, had innate resistance. In the 1950s, approximately 1,000 chemicals needed to be synthesized and tested to discover a new herbicide. Today the success rate for discovering new herbicidal compounds has decreased to one in one million.

As discovering new herbicidal molecules became increasingly difficult, crop developers began to apply the second approach – broadening the capacity of crops to resist herbicides. For centuries, the genetic makeup of crops has been modified to develop new traits through breeding. Some breeding relies on moving existing genes among different crop varieties or from wild relatives to the crop. In other cases, plant breeders must first create novel genes with various techniques that induce genetic variation. Unfortunately, using these standard crop improvement techniques, plant breeders had limited success broadening crop ability to withstand herbicide treatments. 

Without the breakthroughs in modern biotechnology that occurred in the 1970s and 80s, the number of chemical options for weed control would have continued to decline as weeds evolved mechanisms to withstand herbicide applications. The new genetic tools allow crop developers to identify novel herbicide resistance genes that are present in nature and transfer the new genes into crop plants. For a discussion of biotechnology methods used by scientists to develop crop plants, see the Science Narrative 'Methods of Biotechnology' on this website.

Over the past 50 years, DuPont has actively pursued research approaches for increasing chemical weed control options and flexibility. Scientists at DuPont have discovered and developed more than 30 chemicals that have been used to control weeds by growers worldwide. As concerns about the potential effects of synthetic chemicals on environment and health have risen, our chemists have focused on the attributes of herbicides that affect environmental impact and food safety. Over time, the herbicides DuPont has developed degrade more rapidly, can be used at significantly lower doses, are less likely to leach into groundwater and have lower toxicity values when tested on animals.

Today most of the herbicides marketed by DuPont belong to the sulfonylurea class of herbicides, which target a specific plant enzyme.  » More

The sulfonylureas control a wide spectrum of weeds at very low application rates, break down rapidly to non-toxic compounds, and have low toxicity values because they target an enzyme found in plants but not animals. Unfortunately, a number of weeds have become resistant to the sulfonylureas and other herbicides that target that enzyme.  » More

Like other crop developers, our success using traditional plant breeding tools to produce crop cultivars with broader herbicide tolerance has been quite limited. Using corn tissue culture we discovered novel tolerance to an herbicide in the imidazoline class and bred that trait into a number of corn cultivars. Soaking soybean seeds in a chemical that induced genetic variation led to sulfonylurea tolerant soybeans.  

Recently we used modern biotechnology to develop new herbicide resistant varieties of corn, soybean and canola. In addition to marketing crops with resistance to the herbicide classes listed above (sulfonylureas and imidazolines) biotechnology has allowed us to commercialize crops resistant to two additional herbicide active ingredients, glyphosate and glufosinate, both of which have characteristics that minimize impacts on health and the environment.  » More    » More

The new herbicide resistant crops have provided growers with an easy to use, lowcost and effective weed control program that does not harm their crops. In addition, the new herbicide resistant crops, developed with modern biotechnology, have significantly increased growers’ profits by decreasing their input costs, increasing yields, or both, in some cases. Finally, the new herbicide resistant crops have increased no till and minimum tillage agriculture in the U.S. by 35%, which saves one billion tons of soil material from erosion annually.

As a result of these benefits, the rate of adoption of biotech herbicide resistant crops has been quite rapid. Glyphosate-resistant soybeans became available to U.S.growers in 1996, and, within five years, 70% of the soybeans grown in the U.S. were glyphosate-resistant biotech varieties. The rate of increase in Argentina was even more rapid. Within the same time frame, they moved from zero acres of glyphosate-resistant soybeans to more than 29 million acres, which is 98% of the total soybean acres in Argentina. Currently over 60% of the global soybean acres are herbicide-resistant, primarily glyphosate-resistant, varieties. In 2005, 71% (157 million acres) of the 222 million acres of biotech crops planted globally were herbicide resistant varieties of corn, soybean, canola and cotton. The majority of the corn, canola and cotton varieties were resistant to glyphosate. A 2004 summary discussing global status of biotech crops is available on the ISAAA website. [.pdf]

As a result of this remarkable adoption, glyphosate-resistant weeds have begun appearing in fields with row crops like corn and soybean where glyphosate has been used repeatedly.  » More

The effectiveness of glyphosate-resistant weed control discouraged farmers from implementing diverse weed management practices, and lack of diversity in weed control measures encourages the evolution of resistance to a measure that is used repeatedly.  » More

Recently scientists have discovered novel sources of resistance to the sulfonylureas and imidazoline herbicides as well as glyphosate.

All of the glyphosate-resistant biotech crops on the market rely primarily on providing crops with a gene that encodes a glyphosate-insensitive form of the glyphosate target protein.  » More

A novel biochemical mechanism of glyphosate resistance was recently discovered in a naturally-occurring microorganism. This microorganism has a gene for an enzyme that is capable of deactivating glyphosate. Scientists optimized the activity of this enzyme.  Once they transfer the gene for the optimized enzyme into crops, it will effectively protect the crops from glyphosate treatment.  » More

In addition to identifying a new gene for glyphosate resistance, scientists have also discovered a novel source of resistance to sulfonylureas and imidazolines in corn and soybeans. When this mechanism is adequately expressed, the sulfonylureas, imidazolines and a number of other similar herbicides can be applied without injuring the crop. These herbicides, like glyphosate, are highly advantageous to growers because they are effective against a broad spectrum of weeds.  » More

Combining both of these traits in one crop will provide growers with unprecedented flexibility in weed control and a new strategy for controlling their most difficult weed problems.  » More