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Minnesota Department of Agriculture proposes pheromone aerial treatments to slow spongy moth advance into Rochester
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Summary
State officials told the Rochester City Council they plan targeted mating-disruption aircraft applications in late June–early July across three polygons in the Rochester area to suppress early spongy moth populations; staff said residents in affected blocks will receive postcards and a week’s notice before operations.
The Minnesota Department of Agriculture told the Rochester City Council on March 9 that it will propose mating-disruption treatments over three canopy polygons in Rochester in late June or early July to slow the westward advance of spongy moth, an invasive caterpillar that defoliates more than 300 tree species.
Kimberly Keeling Kramer, a manager at the Department of Agriculture, said the department uses a species-specific synthetic pheromone product (SPLAT, described as EPA‑certified and biodegradable) that disrupts male moths’ ability to find females and thus reduces reproduction. She said the approach targets adult moths during a narrow mating period and is intended only for very low‑threshold, early detections.
“We flood the area with very small droplets so the male moths emerge and simply can’t find a female in which to mate,” Keeling Kramer said, explaining the product’s species specificity and that it is dispensed by low‑flying aircraft at a rate designed to minimize non‑target impacts.
Why it matters: staff said the treatment is preventive. Keeling Kramer said the department’s long‑running "Slow the Spread" partnership with the U.S. Forest Service and USDA’s Animal and Plant Health Inspection Service has reduced the natural spread of spongy moth and that early intervention can delay establishment and reduce the need for heavier controls later.
Council members asked for specifics about how the department decides to treat. Keeling Kramer said decisions are based on trap networks and follow‑up ground surveys rather than a single insects‑per‑acre threshold. She said Rochester’s proposed treatment area totals roughly 36,000 acres across three geographic blocks and that Minnesota is proposing to treat about 152,000 acres statewide in 2026.
On safety and notification, Keeling Kramer said the pheromone product is non‑toxic, biodegradable and species specific; the department will provide layered outreach including a local‑government listserv for elected officials, postcards to affected households (about two weeks before), an opt‑in email/text notification for residents, a reminder the night before, and a morning‑of notification once aircraft are active. Staff said aircraft will avoid non‑canopy areas and will shut off booms over water, fields and pavement.
Keeling Kramer and John Larson, the department’s spongy moth treatment coordinator (introduced by staff at the meeting), answered questions about human and tree impacts; they said current detections in Rochester are at a very low level, that tree stress and defoliation typically appear years after management stops, and that other tools (such as Bacillus thuringiensis kurstaki, or BTK) are used if populations rise past mating‑disruption thresholds.
What’s next: staff said they will hold local public meetings (including a March 31 session in Olmsted County and a virtual option for Southeast Minnesota) and will complete additional outreach before any operations. Council members pressed staff for precise dates and committed to relaying official notifications to constituents.
No formal municipal action was taken at the study session; the Department of Agriculture said it will continue coordination with the city and county government and provide more detailed notices as dates firm up.
