Q&As/Citrus or Edibles Plant Diseases/Sooty Mould on Lemon Trees
My lemon tree is covered in this black sooty like stuff? What is it and how do I get rid of it?
From the image you have supplied it looks like you have a fungus problem known as sooty mould which is caused by scale and/or other sucking insects and is a very common problem on citrus. Carefully inspect your tree, especially the undersides of the leaves, and you will see small scale insects adhered to the leaf. These insects suck the sap out of leaves, producing a sticky sweet substance called honey dew which attracts the growth of sooty mould. This mould can cover much of the leaves, reducing the plants ability to photosynthesise, affecting growth and fruit production.
To treat the problem; kill the insects by spraying them with a good quality horticultural oil - good coverage is important, particularly on the undersides of leaves. Once the insects are dead there is no more ‘food’ for sooty mould to grow on so it will begin to disappear. Any fruit that has mould on it is fine to eat; simply remove it by washing the lemons with soapy water. Healthy trees are less prone to pests and diseases so regular watering, feeding and attention is important. Citrus are ‘gross feeders’ so apply Daltons Goldcote Fruit & Citrus Tree Fertiliser just outside the branches’ ‘drip line’ at six-weekly intervals from late October to early December, recommencing late February through to early April.