Berkeley's Polypore Is Peaking This October — Here's What Maple Owners Need to Know

If you have large maple trees on your property, October is the month to pay close attention to what's happening at their base. Berkeley's Polypore (Bondarzewia berkeleyi), a moderate-severity wood-decay fungus, is entering what is typically one of its most active periods of the year. Knowing what to look for — and acting promptly — can make a meaningful difference in how you manage this threat long-term.

Check our seasonal forecast for the latest regional activity updates, or jump straight to the full details on Berkeley's Polypore.

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Why October Matters for This Threat

Berkeley's Polypore has a typical activity window that spans much of the growing season — February through June, and again from September through November. That second wave, peaking in October, is when conditions in the eastern United States often create ideal circumstances for fungal fruiting bodies to emerge and become visible to homeowners.

October is significant for a practical reason beyond biology: the fruiting bodies that appear now are your clearest signal that internal wood decay is already underway. The mushroom-like structures you see at the base of a tree are not the disease itself — they are the reproductive stage of a fungus that has likely been breaking down the wood inside for some time. Spotting them now, while the season is active, gives you the best window to assess damage and take action before winter sets in.

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What to Look For Right Now

Berkeley's Polypore produces large, distinctive fruiting bodies that are worth knowing by sight. Here's what field observations describe:

• Location: Look at the base of large maple trees, right at or just above the soil line.
• Size: Individual caps can range considerably — a younger specimen might measure roughly 8 inches long, 5 inches wide, and 3 inches tall, while mature specimens can reach approximately a foot in diameter. The stipe (stem) can extend several inches below the cap before anchoring into the root tissue.
• Appearance: The flesh is white and does not stain when cut or bruised.
• Smell: A sulfurous scent, sometimes compared to the well-known Chicken of the Woods fungus, may be noticeable.
• Growth habit: Fruiting bodies often appear in overlapping, shelf-like clusters at the base of the host tree.

If you're unsure what you're seeing, use our diagnosis tool to get a faster read on your situation.

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Where It's Active Right Now

Berkeley's Polypore is currently being tracked across a wide swath of the eastern United States. Active states this season include Michigan, New York, Pennsylvania, Ohio, Maryland, Connecticut, North Carolina, Massachusetts, New Jersey, Delaware, New Hampshire, Virginia, Kentucky, Georgia, Maine, Indiana, Alabama, Illinois, and Tennessee.

If your property falls within any of these states and you have mature maples, a walk-around inspection this month is strongly encouraged.

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What to Do This Month

There is no cure for an established wood-decay fungus, but there are meaningful steps you can take in October to manage the situation and protect surrounding trees.

1. Sanitation and Cleanup Remove any visible fruiting bodies and dispose of them — do not compost them. Clear fallen leaves and organic debris from around the base of affected trees. This reduces spore load in the immediate environment. Sterilize any pruning or cutting tools used near infected tissue to avoid spreading fungal material to other trees.

2. Improve Growing Conditions Many fungal pathogens gain a foothold in trees that are already stressed. Check drainage around the base of your maples and correct any areas where water pools after rain. Avoid overwatering. Apply a layer of organic mulch around the root zone — keeping it a few inches away from the trunk — to moderate soil moisture and reduce splash dispersal of spores.

3. Consider Targeted Fungicide Application For trees where infection pressure is high or where you're trying to protect adjacent healthy trees, a systemic or contact fungicide applied at appropriate label rates may be warranted. Repeat applications are often necessary during wet fall weather. Always follow product label directions carefully.

4. Document What You See Photograph the fruiting bodies, note their size and exact location on the tree, and track whether new ones appear. This information is valuable if you later consult a professional.

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When to Call an Arborist

Berkeley's Polypore indicates internal wood decay, which raises legitimate structural safety concerns — especially for large, mature maples near homes, driveways, or areas where people gather. You should contact a qualified professional if:

• Fruiting bodies are large, recurring, or numerous
• The tree shows other signs of decline such as dead branches, crown dieback, or bark abnormalities
• The tree is located near a structure, utility line, or high-traffic area
• You are unsure of the extent of internal damage

An ISA Certified Arborist can assess structural integrity, recommend treatment or removal if necessary, and help you make informed decisions about the tree's future. Find a certified arborist near you through our professional directory.

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October is a short window — don't wait until the fruiting bodies disappear to take action. The fungus will still be there even when you can no longer see it. Acting now is the best thing you can do for the long-term health of your maples.