UVM field trials find mixed benefits from neonicotinoid seed treatments; residues and runoff vary by soil and management

Heather Darby, agronomist and soil specialist at University of Vermont Extension, briefed the committee on two years of field trials intended to inform when variances or exemptions for neonicotinoid seed treatments might be warranted.

"We have not seen any significant differences in plant populations between treated and untreated corn seed," Darby told the committee, describing planning-date trials that planted treated and untreated seed across six planting windows from May 10 into mid-June to capture seed-corn-maggot peak flights.

Nut graf: The trials showed seed-corn-maggot pressure varies by planting date and local conditions; in most cases treated and untreated plots had similar plant populations and yields, though one late planting date showed a meaningful but statistically inconclusive yield drop in untreated plots. Residues of neonicotinoids were detected in some soils and in tile and surface runoff following heavy rain; planter-dust loss in 2024 was low in wet, low-wind conditions but differed by seed brand and fluency agent.

Key findings and details

- Planning-date trials (2023———and preliminary 2024 results):…