Are agricultural best management practices effective at lowering agricultural runoffs in our streams?

We know that crops need three things to grow: soil, water, and sunlight. But to get a plant from a tiny seed to a fruitful crop, a farmer's work is rarely so simple. The field becomes a battleground where hungry insects and competing weeds fight for dominance. To ensure the produce is free of pests and disease-causing organisms, farmers rely on herbicides and insecticides. Rain often washes these chemicals into our waterways, where they can harm fish, insects, and people. Henry Kibuye,a Penn State PhD student in the Biorenewable Systems graduate program, is investigating whether “best practices” typically used to manage other pollutants can reduce pesticide transport into the streams.

“To effectively manage pesticide pollution we have to understand how pesticides move in the environment,” said Henry Kibuye. “This information will help farmers and land managers so they can build ‘pollution checkpoints’ where they can stop the pollution.”

Over the 2023 crop growing season, Kibuye and a team of researchers took grab-water samples and used special passive samplers at each of five stream monitoring sites in Halfmoon Creek Watershed in central Pennsylvania to assess the occurrence of four neonicotinoids (clothianidin, imidacloprid, thiamethoxam and thiacloprid) and two herbicides (atrazine and simazine). Because pesticides rarely travel alone, at each site, the team also measures different nutrients (nitrate, ammonium, phosphate, nitrogen, phosphorus) and sediment. Water levels were tracked with sensors and manual readings to see how streamflow affected pesticide movement.

What the team found was revealing: the pesticide levels changed with the season, location, and how much water was flowing. But the different pesticides showed different transport dynamics . Atrazine and simazine moved alongside the nutrients and sediment in surface runoff. This means some conservation practices that target nutrients and sediment – like vegetative buffers which are strips of plants, shrubs, and trees planted between water bodies and areas of human activity – may also help reduce their transport.

“In areas with good conservation practices, pesticide levels were lower,” Kibuye said. “In areas with heavy row cropping and few buffers, pesticide levels were higher. That tells us where we need to focus our water quality restoration efforts.”

Neonicotinoids showed a different pattern, with high concentrations even during low flows, suggesting they may be transported via groundwater, bypassing treatment by buffers. This highlights uncertainty in buffer effectiveness, necessitating other management practices such as smarter application timing.

The good news? These results suggest that nutrient and sediment buffers likely provide co-benefits in reducing transport for some pesticides. Targeting watershed hotspots (areas with heavy row cropping and few buffers) for buffer implementation can improve water quality for Halfmoon Creek and similar watersheds, benefit aquatic life and provide habitat for terrestrial species like bees and birds.

Henry Kibuye is a 1st year PhD student in the Biorenewable Systems program advised by Dr. Heather Preisendanz. Henry’s research is funded by United States Department of Agriculture (USDA) Grant # 2023-67019-39708. This article was written by Clin Lai, a PhD student in the Cognitive Psychology program, as part of the Fall 2025 INSECT NET SciComm Training Workshop.