Forum home Problem solving

Black Soot



  • I have it on a large pieris is and also adjacent rhododendron (although not too affected). The whole bush - upper and underside of all leaves  branches thickly coated in soot mould. Tried wiping off - failed as too many leaves and treated with mildew killer. Nothing has worked. Will try above suggestions but I'm of the mind now to cut it down to the ground.








  • I have a severe sooty mould problem on both a pieris and an azalea. First time ever. Both well established plants, in separate beds. No overhanging plants.
    Both had a lot of aphids last year, which I struggled to control. From my research, the sooty mould grows on honeydew produced by aphids or other leaf sucking insects and neem oil seems to be the most recommended treatment to control the pests and to help get rid of the mould.
    Neem oil is a natural product that is both a fungicide and insecticide, as well as being good for the plants and kind to earthworms and bees - or so my research would suggest.
    I have bought some cold pressed neem oil - best for the active ingredients, rather than buying something with a bit of neem oil extract in it - along with some garden-friendly emulsifier to help the oil mix with water, and am going to spray my plants as soon as the weather permits.
    Approx 1teaspoon oil and a couple of drops of the emulsifier in a litre of water seems to be the suggested ratio for this purpose, though its hard to find clear advice on this.
    I’ll update this space when I see whether or not it works.
  • Update: i gave the plants the first neem oil spray a couple of days ago. It seems to have loosened some of the sooty mould making it easier to sponge off, and the pieris is already looking a little happier. I cannot find any evidence of insects on it, wondering if it could be lace bugs. Will keep a lookout for any young ones as the spring progresses.
    The azalea is a different story. It is absolutely covered in scale insects. Soft scale, I think. Which explains the sooty mould. Impossible to clean them off every leaf, but neem oil is meant to cover their breathing holes and smother them. Here’s hoping!
Sign In or Register to comment.