Any idea what disease my camellia has?

Looks like it's hitting puberty.

Yeah that fuzz looks like a wooly scale. Imidacloprid will do the job, just don’t wait too long because it can affect bees. Plenty of products available like Bayer’s Tree and Shrub, Protect and Feed.

Appears it might be tea scale. I sprayed my camellias a couple days with imidachloprid, and will apply a imidachloprid or acephate soil drench (systemic translocation through the plant) to them later today. There are other treatment options. Few articles to read.

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Tea scale is the devil. You need a systemic, and you also need to manage the area beneath the camellias. Don’t mulch too deeply, and take steps to ensure good air circulation in the area (ie, trim neighboring shrubs). If those plants are under your drip line, consider installing a short piece of gutter to keep their leaves from constantly being damp from eaves dripping.