Hello all.

Need help identifying what's wrong with my camellia japonica plants.

These are planted in containers. Location/zone: Northern California. Had problems with aphids last year, but a few months ago I started spraying neem oil (diluted per instructions) on leaves once a week. I also spray the same diluted solution on the soil, because I suspected a mold issue. (Had a problem with black sooty mold around the same time as aphids, but that seems to have gone away.)

Question: What is the layer of fiber-and-dirt growing on the surface of older leaves? It look like short fibers... Is it insect poop? Or is it a different variant of sooty mold?

I try to wipe it off the leaves using soap and water, but it always comes back. It seems to only affect older (dark green) leaves, not so much the newer leaves (lighter green), although that seems to be changing for the worse as well.

Help? What is wrong with my camellias? Any advice appreciated.