I have two 55-year-old, gorgeous Japanese red maples - not the ones whose leaves look purplish, but red maples. Anyway, there was a tree knot on one of the main branches. It fell out. Now the area where it was -large size hole - looks very porous and rust color inside. Is it dying? I'd be mortified. I love those trees. Is there anything I can do? What does a tree knot come from, and what does it mean when it falls out? After reading your site (it's very good), maybe we should have kept what fell out and taped it back in. A neighbor said to fill the hole with a contractor's spray foam. Please help.
Certified GKH Gardening Expert
Filling in the hole can cause further damage as it traps moisture and disease. You can treat them with an insecticide and a fungicide (neem oil is nice because it is both) and let them heal over naturally. It is usually better to let it heal itself.