How to get rid of black mould on a lemon tree

Finding black mould on your prized lemon trees can be rather an unpleasant shock, but luckily it looks a lot worse than it really is. In fact this particular black mould, commonly known as 'sooty mildew' isn't actually what you would call a disease at all and does not directly damage the tree or any of its leaves.

Black mould and scale insects on a lemon tree 
Rather than than infecting the lemon tree, the fungus is feeding from a sugary substance that has formed on the plant. This is honeydew and it is the undigested sap of the lemon tree that is excreted from the behinds of aphids and scale insects. So instead of a fungal disease you instead have an insect infestation. Of course in extreme cases a thick covering of sooty mould will affect the lemon tree in so far as it blocks light to the leaves. This can cause stunted growth and yellow its foliage.

Luckily the black mould is easily removed by spraying it with a warm, mild, insecticidal soap solution. Allow the solution to soak in for ten minutes or so and then remove the sooty mould from the leaves by gently washing it off with a soft cloth and some more lukewarm water. If insecticidal soap is not available consider using dish soap, or detergent dissolved in water and sprayed onto the plant. One tablespoon of soap per gallon of water is the usual recommendation.

Of course this does not address the underlying cause of aphid or scale infestation and if you intend to eat the lemons fruit then you must treat the pests organically. Pre-packed trigger sprays containing solutions of naturally occurring insecticides such as rotenone and pyrethrin will be available at all good garden outlets. Applied carefully and always read the manufacturer's instructions.

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