Developing Herbicide-Tolerant Crops

Weeds represent one of the most persistent challenges in modern agriculture, competing with crops for water, nutrients, sunlight, and space. If left uncontrolled, they can reduce crop yields by 20 to 60 percent. For decades, farmers relied on intensive tillage and multiple herbicide applications to manage weeds, but these methods proved costly and environmentally taxing. Then came a breakthrough: scientists learned to engineer crops that could survive applications of powerful herbicides, fundamentally changing how farmers approach weed management.

What are herbicide-tolerant crops? 🔗

Herbicide-tolerant crops are genetically engineered plants that can survive applications of specific herbicides that would normally kill them. These crops contain genes, typically sourced from soil bacteria, that allow them to either tolerate or break down herbicides that would otherwise damage or destroy conventional crops. The most common herbicide-tolerant varieties are designed to withstand glyphosate, a broad-spectrum herbicide marketed under the brand name Roundup.

The concept is straightforward: farmers can plant these modified crops and then spray herbicides over the entire field during the growing season. The crops survive while weeds are eliminated. This approach, known as post-emergence herbicide application, gives farmers unprecedented flexibility in timing weed control without damaging their crops.

The science behind resistance 🔗

The mechanism behind herbicide tolerance centers on a critical plant enzyme called EPSPS (5-enolpyruvylshikimate-3-phosphate synthase). This enzyme plays a vital role in producing aromatic amino acids that plants need to survive. Glyphosate works by blocking this enzyme, effectively starving the plant of these essential compounds.

Bacterial genes to the rescue: Scientists discovered that certain soil bacteria possess versions of the EPSPS gene that are not inhibited by glyphosate. The most widely used gene comes from a bacterium called Agrobacterium strain CP4, isolated from a glyphosate waste treatment facility. When this bacterial gene is inserted into crop plants, it produces an enzyme that continues functioning even when glyphosate is present.

Another approach involves inserting genes that encode enzymes capable of breaking down glyphosate before it can harm the plant. For instance, some engineered crops contain bacterial genes that produce enzymes to detoxify or degrade the herbicide, rendering it harmless to the crop while still eliminating weeds.

Major herbicide-tolerant crops dominating global agriculture 🔗

Three crops account for the vast majority of herbicide-tolerant plantings worldwide: soybeans, corn (maize), and cotton. According to data from the International Service for the Acquisition of Agri-biotech Applications, herbicide-tolerant crops consistently occupied the largest planting area among biotech crops from 1996 to 2018, covering 87.5 million hectares or 45 percent of all biotech crops planted globally in 2018.

Soybeans lead the way, with approximately 93 percent of U.S. soybeans being herbicide-resistant varieties. These crops have been adopted so widely that they’ve become the standard rather than the exception in many agricultural regions.

Corn follows closely, with about 85 percent of U.S. corn engineered for herbicide tolerance. Many modern corn varieties combine both herbicide tolerance and insect resistance traits in what are called “stacked” varieties.

Cotton rounds out the top three, with 82 percent of U.S. cotton plantings using herbicide-tolerant varieties. Other crops engineered for herbicide tolerance include canola, sugar beets, and alfalfa.

Global adoption continues to expand 🔗

The adoption of herbicide-tolerant crops has transformed agriculture on a global scale. Recent data shows that transgenic crops reached 210 million hectares worldwide in 2024, with the United States cultivating 75.4 million hectares, followed by Brazil with 67.9 million hectares.

The rapid growth isn’t limited to the Americas. Countries across South America, Asia, and even parts of Europe have approved various herbicide-tolerant crops for cultivation. Vietnam saw a remarkable 93 percent increase in GM crop area, while Uruguay expanded by 50 percent, demonstrating the technology’s expanding global footprint.

Benefits driving farmer adoption 🔗

The widespread adoption of herbicide-tolerant crops stems from several practical advantages they offer farmers:

Simplified weed management: Instead of applying multiple selective herbicides to control different weed species, farmers can use a single broad-spectrum herbicide. This reduces both the complexity and cost of weed control programs.

Support for conservation tillage: Because farmers can control weeds with herbicides rather than mechanical tillage, herbicide-tolerant crops have facilitated the adoption of no-till farming. According to the American Soybean Association, the shift to no-till practices after planting herbicide-tolerant soybeans saved over 234 million gallons of fuel and left 247 million tons of topsoil undisturbed.

Reduced soil erosion: No-till and reduced-tillage practices preserve soil structure and reduce erosion, contributing to long-term soil health and carbon sequestration.

Flexible timing: Farmers can apply herbicides later in the crop’s growth cycle, giving them more options for managing weeds that emerge at different times during the growing season.

Challenges and the rise of resistant weeds 🔗

Despite these benefits, herbicide-tolerant crops have introduced new challenges. The most significant concern is the evolution of herbicide-resistant weeds. When farmers repeatedly use the same herbicide year after year, they create strong selection pressure that favors weeds naturally resistant to that chemical.

Studies show that the number of glyphosate-resistant weed species has increased dramatically since herbicide-tolerant crops were introduced. By 2012, over 61 million acres of U.S. cropland were infested with glyphosate-resistant weeds, forcing farmers to use additional herbicides or return to more intensive management practices.

Palmer amaranth and waterhemp have proven particularly problematic, with some populations showing resistance to multiple herbicides. This has prompted the development of crops tolerant to additional herbicides like dicamba and 2,4-D, though these newer herbicides bring their own concerns about drift and damage to neighboring crops.

Increased herbicide use: Contrary to early expectations, research indicates that herbicide use on genetically engineered crops has increased over time. Glyphosate use on corn increased from 1.5 pounds per planted acre in 2001 to more than 2.0 pounds per acre in 2010, largely due to the need to combat resistant weeds with higher application rates.

Environmental and ecological considerations 🔗

The environmental impacts of herbicide-tolerant crops extend beyond weed resistance. Some studies have raised concerns about effects on biodiversity, particularly regarding pollinator habitats. The increased use of herbicides in fields planted with herbicide-tolerant crops can eliminate milkweed and other plants that serve as food sources for butterflies and other beneficial insects.

However, supporters point to benefits such as reduced tillage, which decreases fuel consumption and carbon emissions while improving soil health. The debate continues over whether the environmental benefits of reduced tillage outweigh the potential negative impacts of increased herbicide applications.

The future of herbicide-tolerant crops 🔗

As weed resistance continues to evolve, researchers are developing crops with multiple herbicide tolerance traits stacked together. These next-generation varieties can tolerate several different herbicides, allowing farmers to rotate among different modes of action and slow the development of resistant weeds.

Scientists are also exploring new gene-editing technologies like CRISPR that could create herbicide-tolerant crops without introducing foreign genes. These approaches may face fewer regulatory hurdles and gain wider public acceptance than traditional genetic engineering methods.

The success of herbicide-tolerant crops ultimately depends on implementing integrated weed management strategies that combine these tools with crop rotation, cover crops, and other practices that reduce reliance on any single herbicide. Without such stewardship, the utility of even the most advanced herbicide-tolerant crops may be short-lived.

What do you think? How can farmers balance the convenience and benefits of herbicide-tolerant crops with the need to prevent weed resistance? What role should newer gene-editing technologies play in developing the next generation of these crops?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC3145815/
2. https://www.isaaa.org/resources/publications/pocketk/10/default.asp
3. https://www.seedworld.com/latam/2025/07/21/adoption-record-transgenic-crops-reached-210-million-hectares-in-2024/
4. https://extensionpublications.unl.edu/assets/html/g1484/build/g1484.htm
5. https://serc.carleton.edu/integrate/teaching_materials/food_supply/student_materials/1189
6. https://enveurope.springeropen.com/articles/10.1186/s12302-016-0070-0