The future of bioherbicides
Weeds present a major problem for all who cultivate crops or manage landscapes.
In the mid-1900s, developers figured out how to manage weeds with chemicals—a broad solution that has been widely adopted. However, the problems that emerge with chemical herbicides are now presenting in what might be called a perfect storm: herbicide resistance in weeds, exposure of toxins to farmers and the environment, aerial herbicide drift, consumer backlash against pesticides, and lawsuits. Combined, these have significantly impacted the ag/chemical industry.
Until the availability of chemical herbicides, there was a science of integrated weed management that included crop rotation and tilling. This is still the state of the art in developing countries. Chemicals were useful and labor saving because they were broad spectrum to the point where the farmer no longer had to even know the name of the weed. In time the chemical industry found that they should target single sites of action (enzymes). For example, the herbicides glyphosate and imazapyr inhibit the top enzymes of essential amino acid biosynthesis, and by inhibiting these enzymes, plants are deprived of the amino acids needed to make protein. The fact that there are mutant plants (both crops and weeds) that are resistant to these single site of action chemical herbicides is a double-edged sword. If the crop is resistant, then the agrichemical industry benefits by selling the herbicide AND the resistant seed. However, the weeds have also developed resistance (glyphosate damaged all weeds when it was released in the 1970s, but now dozens of weeds are resistant).
Until the availability of chemical herbicides, there was a science of integrated weed management that included crop rotation and tilling. This is still the state of the art in developing countries.
While bioinsecticides and bio fungicides are dominant in the biopesticide market, few bioherbicides have yet been commercialized. Mark Trimmer of Dunham Trimmer (the premier market research company on global biological agriculture markets), has specifically pointed out this absence while projecting that biocontrol (including bioinsecticides and biofungicides) is projected to exceed $10 billion annually by 2025. The absence of bioherbicides is not due to lack of demand, but rather the challenge in finding effective and economical bioherbicide solutions.
Let’s look at a biological solution for a biological problem. Several generations of plant pathologists did attempt to try killing weeds with their favorite fungi. Diseased weeds were found in nature. However, some of the most promising fungi for weed control were not virulent enough (at best they have a 40% mortality rating against a weed, and to compete head to head with chemical herbicides they need a 95% mortality index). Fortunately, we’ve found a way to solve this problem—a way to select the most virulent native fungi—opening up a new world of weed management.
Bioherbicide development background and prospects
Why
Our goal is to manage weeds, while avoiding chemical herbicides, for healthier ecosystems, humans, and supply chains.
What
Our virulence-enhancement technology selects the most virulent strains of pathogenic fungi. These fungi (Fusarium oxysporum) are host specific (meaning they will only attack their host weed) and nontoxic (in fact, they exist in the field naturally). They can be locally sourced and inexpensively manufactured.
Proof of concept
In sub-Saharan Africa, a parasitic plant called Striga (witchweed) attacks maize, rice, millet, and sorghum—the staple food crops for subsistence farmers—on 40 million farms annually (leading to approximately $10 billion in crop loss). These smallholder farmers, with very little acreage, were not a viable market for synthetic chemicals.
Using locally sourced fungi, we selected for the overproduction of specific amino acids. By way of fungi coated toothpicks as our delivery mechanism, a fresh field inoculum is made at the village level with a rice-based inoculum substrate that gets planted with each seed. The Bill and Melinda Gates Foundation funded trials on 500 farms, resulting in an average crop yield increase of 56%.
Called the Toothpick Project, we have launched a social enterprise in Kenya and trained a science team from 13 African countries to scale up the initiative.
Next Steps
Flip the world of plant pathology! Pest management can be a new business model. Imagine vaccinating your soil rather than dosing it with chemicals.
Let’s look at the world’s worst weeds. We started with the greatest weed threat to global food security. Now, in the US we are working on using Fusarium for field bindweed and Canada thistle. We have a growing list of other target weeds.
Regulatory hurdles are cumbersome and time consuming (five years in Kenya). We are currently serving as a case study for a grant proposal researching the harmonization of biocontrol regulations in African trade zones.
There are a variety of methods for distribution. Currently we’re testing seed coating and fresh field inoculum.
We are building the knowledge—for both the scientific world and the public—on the vast benefits and opportunities of this innovation.
