Black-Staining Polypore Is Peaking This October — Here's What Homeowners Need to Know

If you've noticed unusual fungal growth at the base of trees or along roots in your yard, October may be the worst time to ignore it. The black-staining polypore (Meripilus sumstinei) is entering peak activity this month, and it's currently confirmed active across a wide swath of the eastern United States. Understanding what this fungus is — and acting quickly — can make a real difference for your trees. Check our seasonal forecast to stay ahead of emerging threats in your area.

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Why October Matters for This Threat

Based on typical activity patterns, black-staining polypore tends to be most active from late summer through late fall, with September, October, and November representing some of its most productive months. October sits squarely in that window — and with the combination of cooling temperatures, increased rainfall, and the natural breakdown of organic matter that comes with leaf drop, conditions this month are particularly favorable for fungal activity.

This is also the time of year when many homeowners are focused on raking leaves and putting the garden to bed, which means tree health can fall off the radar. That's precisely when fungal pathogens can go unnoticed until significant damage has already occurred. Don't let October's distractions work against you.

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What to Look for Right Now

Black-staining polypore is a wood-decay fungus. When inspecting your property this month, get into the habit of walking the base of your mature trees — especially hardwoods — and looking closely at:

• The root flare and base of the trunk — Look for shelf-like or fan-shaped fungal fruiting bodies emerging at or near ground level.
• Exposed roots and nearby soil — Fruiting bodies can appear along surface roots radiating out from the trunk.
• Cut stumps or buried wood — This fungus is associated with wood decay and may appear near old stumps or woody debris.
• Any dark staining — As its name suggests, the black-staining polypore can cause characteristic dark discoloration on wood it infects.

If you're not sure what you're looking at, our diagnosis tool can help you identify what you've found and assess next steps.

> Severity rating: Moderate. This fungus warrants attention and timely action, but a prompt response can help protect your trees. View full details on black-staining polypore for more information.

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Where It's Active This October

Research-grade observations confirm that black-staining polypore is currently active in the following states:

Alabama, Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, and Virginia.

If you live in any of these states, now is the time to be proactive. Conditions across much of this region — with typical fall moisture and cooling nights — are consistent with the kind of environment this fungus thrives in.

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What to Do This Month

October is an actionable month. Here's what to prioritize right now:

1. Sanitation and Pruning Remove any infected material you can safely reach — dead branches, fallen debris, and any visible fruiting bodies. Bag and dispose of this material rather than composting it. If you're pruning, sterilize your tools between cuts to avoid spreading fungal spores to healthy tissue. Improving air circulation by thinning dense canopy growth also reduces the moist conditions fungi prefer.

2. Soil and Moisture Management Fall rains are coming, and standing water near tree bases creates ideal conditions for wood-decay fungi. This month, check that the soil around your trees drains properly. Avoid overwatering if you're irrigating, and consider applying a layer of mulch around the root zone — keeping it a few inches away from the trunk — to moderate soil moisture and reduce fungal spore splash from the soil surface.

3. Fungicide Application If you've observed signs of infection, a systemic or contact fungicide applied at the first sign of activity may help. Repeat applications can be necessary during prolonged wet weather. Always follow the product label carefully for rates and timing. When in doubt, consult a professional before applying any chemical treatment near tree roots.

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When to Call an Arborist

Not every situation calls for a professional, but some do — and sooner is almost always better when it comes to tree health. You should find an arborist and schedule an evaluation if:

• You've found fruiting bodies at the base of a large or mature tree
• The tree shows signs of decline such as thinning canopy, dead limbs, or leaning
• You're unsure whether what you're seeing is black-staining polypore or something else
• The affected tree is near a structure, walkway, or area where failure would pose a safety risk

An ISA Certified Arborist can assess the structural integrity of the tree, confirm the diagnosis, and recommend a treatment plan tailored to your specific situation.

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October is short — don't wait until November to act. A quick walk around your property this weekend could be one of the most valuable things you do for your trees this fall.