Hoes to Herbicides: Reflecting on the last century of weed control and preparing for the next

By Braeden Van Deynze, a PhD student working with Dr. Scott Swinton in the Department of Ag Food & Resource Economics at Michigan State University. Dr. Swinton is also one of the lead scientists with the Kellogg Biological Station Long-term Ecological Research (KBS LTER) program. Here Braeden explains their work taking a long-term view of weed management in the United States, in press in the European Journal of Development Research.

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Since the dawn of agriculture, farmers have done battle with weeds. These unwanted pests grow in competition with crops, siphoning off nutrients, water, and sunlight. For millennia, the primary way farmers combatted weeds was brute force. Their weapons of choice were the hand hoe and field cultivator, wielded by armies of laborers and occasionally assisted by draft animals.

Controlling weeds in such a way was difficult and costly. Over the last century, row-crop farmers in the United States have moved beyond these manual methods. Today, nearly all acres of field corn and soybeans are treated with herbicides, typically in conjunction with traited seeds bred to resist the most powerful formulations.

Dr. Scott Swinton, MSU professor and KBS LTER scientist, and I recently wrote a paper examining the economics and history behind why American farmers have adopted these methods with such enthusiasm. We find that the history of American weed control can be divided into four distinct eras driven by three waves of cost-reducing innovation. The first innovation was the introduction of the tractor in the 1930s. An investment in a tractor allowed farmers to cultivate more land more quickly for a fraction of the labor cost of manual hand hoeing. This development was soon followed introduction of chemical herbicides, a result of a boom in chemical research during and following the Second World War. These chemicals were rapidly adopted because they allowed farmers to reduce the number of passes over each field, substituting man-hours with chemical inputs.

The final wave of innovation was the introduction of herbicide tolerant (HT) crops, which are a vital tool enabling modern weed control systems. HT crops have genetically engineered tolerance to broad-spectrum herbicides such as glyphosate, the active ingredient in Roundup. Farmers who use HT crops can use herbicides to control weeds at any time during the growing season without worrying about damaging their crop. This increased flexibility allows them to use less chemicals because they can eliminate weed competition only when their crop is most vulnerable. The resulting weed control system is cheaper in both chemical costs and labor costs.

Our conclusion is that farmers have adopted herbicides so rapidly because it saves them both time and money.  Innovation has allowed for the substitution of labor, which has become increasingly expensive over the last century, with technologies such as tractors and herbicides. These new technologies have changed the way that farmers manage their land, and in turn their ecosystems.

Today, American row-crop farmers are beginning to face new challenges in weed control. HT crops have allowed farmers to rely on just a handful of herbicides. As a result, many weeds have adapted, evolving resistance to these chemicals, reducing their effectiveness. While previous revolutions in row-crop weed control have resulted from the introduction of new cost-reducing technologies, the next round of innovations must respond to the unintended consequences of the last round.

One possible strategy for dealing with this emerging weed control problem is an increased use of biological control. Farmers can manage their non-crop habitat to promote populations of insects that damage weeds but not crops. This ecosystem-based approach might reduce reliance on chemicals, reducing the risks of groundwater contamination, off-field chemical drift, and the emergence of herbicide resistant weeds. Biological control relies upon natural enemies to reduce the frequency that weed populations reach a problem level, reducing the frequency of herbicide use. But unless farmers view these practices as cost-efficient compared to their current ones, they are unlikely to gain widespread adoption.

Developing new weed control solutions will require new research from agronomists, ecologists, evolutionary biologists, and social scientists. We must work to understand hidden costs of popular weed control practices, like the emergence of herbicide resistant weeds, and propose solutions that work for both farmers and ecosystems over the long-term.