Minnesota Department of Agriculture details detection, quarantine and management after emerald ash borer found in Itasca County

Jonathan Ostos, Emerald Ash Borer technical assistance coordinator for the Minnesota Department of Agriculture’s (MDA) Plant Protection Division, held a virtual informational meeting after the recent detection of emerald ash borer (EAB) in Itasca County and reviewed what residents and land managers should look for, how the state is regulating movement of potentially infested material and options for managing trees.

The meeting laid out why the discovery matters: EAB is an invasive metallic wood-boring beetle that has killed large numbers of ash trees across North America and now occurs in much of Minnesota. Ostos said the MDA has added an emergency quarantine around the new find to limit human-assisted movement of ash wood, firewood and mulch and described how landowners, communities and businesses can detect infestations and respond.

EAB life cycle, host trees and detection Ostos summarized EAB biology and detection: adults typically emerge in late spring to summer, and the agency tracks emergence using growing degree days (about 450 GDD with a 50°F base). Females lay roughly 60 to 90 eggs; larvae feed under the bark in S-shaped galleries that disrupt water and nutrient transport and eventually girdle mature ash trees. In Minnesota the pest can have a one- or two-year life cycle depending on climate, and populations often reach damaging levels within several years after establishment.

He emphasized the most reliable field signs: the S-shaped larval feeding galleries under the bark and larvae with two small spine-like projections near the tail end. Surface signs that help people detect EAB from the ground include woodpecker “blonding” (patches of removed bark), shallow dime-sized woodpeck holes within those blonded areas, vertical bark splits that reveal galleries, thinning of the upper canopy and, on large trees, D-shaped emergence holes created by adult beetles. Ostos cautioned that many early infestations are cryptic and that branch sampling or close inspection of mid-to-upper canopy branches is sometimes required.

Distribution and mapping The MDA maintains a publicly updated map showing confirmed detections and a “generally infested” polygon built as a buffer around confirmed points to represent cryptic spread. Ostos said EAB was first found in St. Paul in 2009 and, as of his presentation, has been confirmed in the majority of counties in Minnesota; the new Itasca County detection was reported near Pokegama Lake, about five to six miles south of Grand Rapids. He noted other recent detections in the region, including a February finding near Virginia, Minnesota, and encouraged residents to report suspicious signs to help improve mapping.

Emergency quarantine and regulated materials Ostos explained that the emergency quarantine for Itasca County (and quarantines elsewhere) aims to reduce long-distance human-assisted spread by restricting movement of regulated articles: any life stage of EAB, ash wood material, hardwood firewood (defined as wood cut to lengths of 4 feet or less) and most unprocessed mulch. The quarantine distinguishes: internal movement within a contiguous quarantine area (allowed), transit through quarantine counties without overnighting loads (allowed with restrictions), and movement from quarantined counties to non-quarantine counties (restricted unless a compliance agreement is in place).

Compliance agreements and treatments to move material legally include grinding or chipping mulch to particles under roughly 1 inch by 1 inch, deep debarking that removes about a half-inch of sapwood, heat treatment of firewood to a core temperature of 140°F for 60 minutes, kiln drying or fumigation. Ostos said the MDA maintains a list of certified heat-treated firewood dealers. He also noted the state’s spongy moth quarantine (Lake and Cook counties) imposes separate restrictions on movement of firewood.

Management choices for landowners and communities Ostos laid out two broad management strategies: removals and insecticide treatments. For high-value shade trees in landscapes, systemic insecticides can prevent or suppress infestations if trees remain healthy enough; he said a common professional treatment (emamectin benzoate) is applied by licensed applicators via trunk injections and is typically guaranteed for two years, with many communities considering a two- or three-year rotation to protect selected trees. He said professional treatment costs commonly observed were about $10 per diameter inch, and that homeowner products are generally not appropriate for large mature trees.

Timing and safety: avoid active season work when possible The MDA recommends avoiding pruning, removal or stump work on ash during the active flight season (May 1–Sept. 30) where feasible because working on infested trees can disperse adults and accelerate local spread. When work must occur in the active season, Ostos advised chipping material before moving it or covering loads during transport; where feasible, perform removals in the inactive season (Oct. 1–Apr. 30). In heavily infested areas year-round work and other disposal strategies may be necessary.

Community planning and resources Ostos urged communities and private woodland owners to inventory ash resources, prioritize removals for poor-quality or hazardous trees, consider targeted short-term treatment programs to slow mortality surges and plan replanting with non-ash species. He identified resources: Minnesota Department of Natural Resources community forestry and stewardship programs, University of Minnesota Extension guidance for managing ash woodlands and MDA guidance and mapping. He advised private woodland owners to contact their local DNR forester for site-specific plans and noted periodic grant opportunities through DNR Community Forestry for inventories, management plans and replanting.

Reporting and next steps Ostos asked attendees to report suspected infestations with clear photos that show woodpecker damage, bark splits, galleries or the insect itself. He described reporting options including EDDMapS and the MDA’s “Report a Pest” online form; such reports automatically include GPS location when submitted through some tools and prompt MDA follow-up. He also said the emergency quarantine rule was in a public comment period through Sept. 8 and that Mark Abrahamson, the state plant health regulatory official, was the contact for input on the proposed quarantine. The presentation was recorded and the MDA planned to post it to its YouTube channel.

The meeting included time for questions; no formal votes or policy changes were taken at the session. The MDA encouraged landowners, arborists and local officials to use the agency’s map and reporting tools to help track and manage the new detection in Itasca County.