I don’t know if I’ll be able to trim it or not because it’s a large piece of wood and I attached plants and such to it already.Any of the driftwoods will mold over if left above the water line in humid conditions. I was soaking a few buckets of new purchased wood (including mopani) and had forgotten about them, and the tips sticking out looked the same.
I boiled mine cleaned and made sure they were completely submerged after. It is mold so it could be bad for you, not sure it would impact the fish any.
Can you trim it down to the water line? If you like the look of it above water and aren't worried about it, you may just need to wait out the mold. At some point it should run out of food and die off.