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April 14, 2025
It's time to give oaks space
Oak wilt is a deadly disease that impacts all Minnesota oaks. Once the non-native fungus infects an oak through a fresh wound, it spreads to nearby oaks through roots. Above ground infection starts on fresh wounds, which attract sap-feeding beetles that carry the fungal spores. Avoid wounding, cutting, or pruning oaks April through July, and you’ll be preventing potential oak wilt (and saving a lot of money on tree removals or control treatments).
- Learn the nuances of preventing oak wilt on pages 4–6 in our detailed oak wilt guide.
- Learn how and where to report oak wilt at the bottom of our oak wilt homepage.
This bur oak died over the course of one summer from oak wilt that started from the wound at the trunk base (circled), made in late May or early June 2024.
Spruce budworm rolling in northern St. Louis, Lake, and Cook counties
Spruce budworm defoliation results in vast mortality of balsam fir and slightly less for white spruce. A native moth/caterpillar, it goes through predictable outbreaks when there is an abundance of older balsam fir present.
- Major defoliation and tree death have occurred in recent years and will continue in 2025.
- Areas with the most noticeable defoliation and mortality will be in northern St. Louis, Lake, and Cook counties.
- Learn more about spruce budworm and management at our spruce budworm homepage.
- Download a homeowner guide for spruce budworm.
 Spruce budworm defoliation on white spruce.
Forest tent caterpillar population increasing slowly but surely
Forest tent caterpillar feeds on various species of hardwood trees, most noticeably on basswood, oak, and aspen in late May and early June.
- We predict that forest tent caterpillar activity in 2025 won’t be widespread and severe, but we do expect more defoliation and caterpillars than in 2024.
- Caterpillars and defoliation will be noticeable in an area from Mille Lacs and Kanabec counties northward to central Itasca and St. Louis counties.
- Learn all about forest tent caterpillar from this fact sheet.
Nearly full-grown forest tent caterpillars munching on basswood in late May 2024.
Recent emerald ash borer finds in Aitkin, St. Louis, and Pine counties
In recent months, emerald ash borer (EAB) was detected in southwest Aitkin, central St. Louis, and northern Pine counties. Make a plan for reducing this ash-killer's impact in a yard, town, or woodlot.
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