Letting the Soil Do the Work: Rethinking Weed Control

For organic farmers, weeds represent the single greatest challenge to profitable production. Since they can’t use synthetic herbicides, they're forced to rely on mechanical cultivation and cover crops for weed suppression which can take a lot of time and forethought. What if the solution wasn't about working harder against weeds, but working smarter with the soil? That's the question driving research in Dr. Carolyn Lowry's lab at Penn State's College of Agricultural Sciences, where her team is investigating ecological weed management from multiple angles, such as how we can design crop communities to suppress weeds, or leverage soil biology to kill weed seeds in the soil.   

Lowry's work is part of Pennsylvania State University's broader Cover Crop Cocktails experiment, which examines how cover crops can better perform a range of different ecosystem services. Within this project, Lowry and her team aim to answer the question: How do different crop plant communities influence weed communities? Their research explores whether planting diverse cover crop or perennial forage mixtures could naturally suppress problematic weeds, such as giant foxtail or Canada thistle, while also providing nitrogen and other ecosystem benefits.  

Lowry's lab doesn't stop at above-ground solutions. A second major research focus examines what happens below the surface of the soil. Her team is studying microbes in the soil that may infect and kill weed seeds, and how different soil management practices might increase weed seed mortality. "We know that soil microbes are a key component of soil health. However, we know very little about which microbes in the soil may help suppress weeds, and whether certain management practices can increase their abundance or activity." Lowry said. The research tests whether certain soil amendments and crop rotations can shift soil conditions to accelerate the rate at which weed seeds die in the soil, and suppress weed populations before they ever emerge. 

The research focuses on three problematic weed species: giant foxtail, common ragweed, and smooth pigweed. These weeds were selected because they're difficult for organic farmers to control and persist in the soil seedbank for years, meaning a single weed plant can cause problems for seasons to come. By understanding how to target these weeds at their most vulnerable stage, as dormant seeds in the soil, Lowry's work offers an approach to long-term weed management. 

This dual approach looking at both plant diversity above ground and soil biology below reflects Lowry's work on tackling weed problems. Rather than asking only, "How do we kill weeds?", her research asks broader ecological questions: "How do we create agroecosystems where weeds don't thrive?" The lab conducts experiments both at Penn State's research facilities and on organic farms across Pennsylvania, ensuring that findings translate into practices farmers can adopt. 

By understanding how plant communities and soil health influence weed populations, Lowry's work helps farmers plan more resilient crop rotations that increase plant diversity, boost ecosystem health, and reduce their dependence on expensive inputs all while cutting labor costs. Some of the best tools for managing weeds may already exist in healthy soil and diverse plant communities; farmers just need to understand how to leverage them.