Nature Lab

Resource Science

Slowing Insecticide Movement in Soil

Neonicotinoids (also called neonics) are a common type of insecticide, often applied to corn and soybean seeds. They protect plants, but when carried by rainwater into streams and other habitats, neonics can harm beneficial insects and other nontarget species.

“Only about 5 percent of neonicotinoids is taken up by the crops,” explains U.S. Geological Survey (USGS) ecologist Lisa Webb. “So, the residual 95 percent is left to move around in the soil.”

To learn what might keep residual neonics from moving into nontarget ecosystems, MDC partnered with University of Missouri researchers to study how one neonicotinoid — imidacloprid — interacts with soils from different habitats.

First, the team randomly selected six sites from MDC conservation areas where crops are planted. Then, at each site, graduate researcher Laura Satkowski collected soil from crop fields, grass buffer strips, and nearby riparian areas (streams or rivers lined with trees) and brought the soil back to a lab for chemical analyses and experiments.

Results showed that imidacloprid passed most quickly through crop soil and most slowly through soil from wooded riparian areas. Organic carbon was a key factor. The more organic carbon in the soil, the more imidacloprid was retained rather than being carried away in water. Soil from grassy and riparian buffer areas contained more than twice as much carbon as soil from crop fields.

“This study shows the importance of protecting and expanding riparian corridors as well as woody draws to help keep these chemicals out of aquatic ecosystems,” says retired MDC Environmental Resource Scientist Doreen Mengel. “Similarly, planting grassy strips along the edges of crop fields can help, and including cover crops in crop rotations can add carbon to the soil.”

Neonicotinoid Movement in Soil at a Glance

Imidacloprid (a neonicotinoid pesticide) moves more slowly through soils with more organic carbon and most easily through soils with little carbon, such as the soil in many crop fields.

MDC Partners

University of Missouri School of Natural Resources and USGS Missouri Cooperative Fish and Wildlife Research Unit