Tried to hose it off, but to no avail, help, Steve.
28 September 2011 11:08 AM
Sooty Mould on a lemon tree occurs when insects such as aphids and scale are present. As the insect feeds it exudes a sugary substance on which the Sooty Mould grows. Unfortunately is is difficult to remove the mould. Once the scale or aphids are treated the mould will no longer form. PestOil can be used to control these pests. I have attached the link to the Yates website which shows the common insect pests that attack citrus. Have a look at the tree and you may find some scale on the leaves or stems. Also, you can try to spray the tree with Yates Nature's Way Citrus & Ornamental Spray.