My Camellia x williamsii 'Donation' made it through the harsh winter with flower buds intact, but the leaves are heavily infested with sooty mould. It is fairly open rather than bushy and isn't a huge plant, but it is about 7' tall x 4' wide, so washing each leaf by hand would take hours and also require standing on a ladder to reach the upper branches. I'll do that if necessary, but is there any easier way of getting rid of the mould - it looks ugly and I think is affecting the plant's health. If I manage to kill the mould with a spray, will the residue then wash off easily or does it need to be physically scrubbed off. If I do have to clean the worst leaves by hand what treatment and tools should I use to get rid of the mould? Will dish soap or vinegar work or do I to purchase something designed to kill mould. Will a sponge be enough? a soft scrub brush? a Lee Valley mushroom brush? From past attempts the mould seems very firmly attached and I don't want to damage the leaf cuticle. Is there something I can do to prevent the mould from returning?
The sooty mold is a byproduct of an insect infestation, likely Scale. The mold essentially grows on the honeydew secretions from the insect. sooty-mold-on-camellia.htm
"Sooty molds are associated with sucking insect pests (aphids, scales, mealybugs, psyllids) that extract sap from the phloem tissue. Soon after a plant is heavily infested with such a pest, it is usually covered with honeydew." https://content.ces.ncsu.edu/sooty-...e associated with,of sap to extract nutrients. (This is just one of many websites that discuss sooty mold.) Camellias seem to be especially susceptible to this problem, perhaps because they attract aphids in particular and have evergreen leaves. From what I know, washing individual leaves is the most effective way to remove the mold but perhaps you don't have to wash all of them. Older leaves will drop off eventually. Going forward, you will have to determine what insect is creating the honeydew and take steps to eliminate it.
One scale insect that is particularly attracted to Camellias is appropriately called Cottony Camelia Scale. It is quite easy to identify; just look up images on the Web. I had sooty mold and scale on an old Camelia that I recently removed and replaced with another variety. It should be easier to prevent the sooty mold than to clean it off, now that I know what to look for.
In my experience, aphids are more likely to be implicated in the sooty mould issue than scale or other sap-sucking insects. It is, in my opinion, much easier to control than scale for example. Many years ago, I was able to eradicate scale from a 5-foot Harry Lauder's Walking Stick before the leaves unfurled by scraping off every little scale mound I could find. It was very, very time consuming. There are other methods too but those usually involve unpleasant chemicals. Aphids, on the other hand, can be dealt with in a number of ways; easiest of all by simply hosing the undersides of the leaves on a regular basis. In short, @dt-van, I hope that you will find that aphids, not scale, are the culprits for your sooty mould problem.
Thanks for the advice, I will certainly check tomorrow to see if it is aphids or not. I did try hosing last year to little effect. It might have killed the insects, but it didn't remove the black coating. If it turns out to be scale I will try neem oil to kill the scale and then wait a couple of weeks before hosing or brushing/sponging to get rid of the sooty mould. It seems like spring temperatures are ideal for oil treatment. In future I will pay closer attention and treat the insect problem right away.
