Maple Trunk Cavity with White Fungus: Internal Decay—Manage, Don’t Treat

The white fungus in the 3-inch knot hole is the fruiting body of a decay fungus rotting the heartwood. This is a terminal condition, but the tree may live many years with good care.

What Not to Do

• Do not fill cavity with concrete—it traps moisture and accelerates decay.
• Do not try to seal or shield the hole—drying it won’t slow decay.
• Do not spray fungicide—it won’t reach the fungus inside the wood.

What to Do

• Break off the fungal conk if bothersome.
• Fertilize: 10-10-10 at 1 lb per inch trunk diameter, fall and spring.
• Monitor for increasing deadwood; plan for eventual removal if structural risk grows.

The tree’s health (green, full canopy) matters more than the cavity.