My Camellia 'Donation' flowered beautifully this year, but I see that many of the leaves are heavily covered with sooty mould. I'm concerned because it is in a pretty shady spot and I figure it needs all its leaves to photosynthesize. I've never noticed aphids on the camellia and this years new leaves don't feel sticky (yet), but it is under a large (rather unhealthy) flowering cherry, which could be a honeydew source. The adjacent rhododendron also has a few leaves with sooty mould. I tried scrubbing the mould off with a toothbrush and warm soapy water, but that stuff really clings to the leaves - it took me about 10 minutes to clean a dozen leaves. Admittedly it has been sunny for a few days so the mould may have been especially dried out, but surely there is a better way. Am I really going to have to hand scrub each leaf? Should I spray the whole plant with plain water and leave it to sit for an hour or two bit before attempting a cleaning? Should I be using something other than soapy water? Once I get it clean, how can I keep it that way?