UVM Extension research finds farm practices, not consistent seed-treatment benefit, drive some pest risks; untreated-seed availability a concern ahead of ban

Heather Darby, an associate professor with UVM Extension, told an unnamed legislative committee on Jan. 27 that recent multi‑site research shows farm practices — notably spring tillage combined with manure and plow‑down cover crops — strongly increase the probability of seed corn maggot damage, while average differences between neonic‑treated and untreated seed were not observed across all trial sites.

"That probability of a farm seeing seed corn maggot damage ... in 2025 was over 80 percent" in fields combining tillage, manure and cover crops, Darby said, noting that high damage probability does not necessarily mean crop failure. "This does not mean the farm is gonna see a crop failure," she added, explaining that high planting populations can allow remaining plants to compensate for losses.

Darby described a three‑year project that placed paired acres of treated and untreated seed at on‑farm sites across Vermont (eight fields in 2024; 15 in 2025, including one research farm) and deployed sticky traps April–July to monitor adult seed corn maggot flights. Across those sites she said the team "did not see any difference in corn populations between neonic‑treated and neonic‑untreated for seed corn maggot," although some individual farms showed substantial wireworm and grub damage that did differ between treated and untreated plots.

"If we look at the average across all these farms, there is no difference," Darby said. "If we look ... the goal right now is to figure out where the risk is. It's not to look at 50 farms, average the numbers together, and say there's no point. It's to look at each individual farm and figure out when, if there is an issue and there is risk, where is it making a difference?"

Committee members pressed Darby about the practical implications of the results and about preparedness for a statutory ban the presenter said is already in place. In the discussion Darby and senators raised three immediate concerns: where untreated seed suitable for Vermont will be available, whether alternative seed treatments will perform in the state's short season and heavy soils, and how to reduce pollinator exposure during planting.

Darby said availability of untreated seed and appropriate genetics is a major worry for farmers. "The bigger risk and concern that farmers have is what seed will be available to them," she said, noting many seed varieties are sold pretreated and that Vermont's short growing season means farmers rely on specific genetics that may be harder to obtain untreated.

On alternatives, Darby described options including diamide seed treatments and applying insecticide through planter fertilizer tanks; she said diamides work but are less widely available and more costly, which likely limits their current adoption. She also reviewed historical on‑planter insecticide use and said many older chemistries are now banned.

Darby emphasized the route by which neonicotinoids have been shown to affect pollinators: abrasion‑generated dust from planters, commonly called "dust‑off," which can carry seed coating particles into the air during planting. Her team tested fluency agents and planter modifications to reduce those emissions and reported promising results with a Bayer fluency agent that substantially reduced planter dust in their trials. "It reduced the dust coming out of the planter quite substantially," she said, while noting availability is still being evaluated.

She also advised that planter type and maintenance matter: some modern planters with vacuums emit very little dust, while older equipment can create measurable dust emissions. Proper maintenance (functional vacuums and upkeep) is a near‑term mitigation step.

The committee sought clarity on whether observed pest damage had translated to yield loss. Darby reiterated growers can experience significant pest pressure without measurable yield declines if plant populations are high; she gave the example that dropping from 34,000 to 32,000 plants per acre may not reduce yield, whereas losses from a lower base population could.

Darby said the research uses conventional statistical thresholds (95 percent confidence) and the project now focuses on analyzing individual farm histories and practice combinations to identify high‑risk circumstances where an exemption or targeted intervention might be warranted under the law. "We're trying to figure out where the risk is and when we should provide exemption," she said.

Committee members thanked Darby and asked her to return to present additional work, including tile drainage research relevant to adoption of no‑till practices. The committee moved on with its agenda after scheduling follow‑up presentations.