What’s holding bioherbicides back?

For the past few decades, farmers have relied heavily on synthetic herbicides like glyphosate, dicamba, and 2,4-dichlorophenoxyacetic acid to kill weeds. But over time, weeds evolved to tolerate those chemicals, and farmers are struggling to keep them at bay. Several start-ups are now developing herbicides made from fungi, microbial metabolites, or plant extracts to help farmers control these herbicide-resistant weeds. They say their products employ new weed-killing mechanisms to address weeds that chemicals can't eliminate. But bioherbicides face huge challenges. They can be expensive, inconsistent, or narrowly focused on a single weed species. A few years ago, Peter Nyamgero retired from a career as a computer repair technician in Nairobi, Kenya, and moved to the country to start farming. He bought a 1 hectare (ha) plot near the border with Uganda that hadn't been cultivated for more than 20 years. But soon after planting his first crop of corn, weeds