Black Mould and Scale on Gardenias

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Question by: Jeff T:

I have some Gardenias with a black mould/scale on the top of the leaves. What is it, and what is the best way to remove it?

Sarah's answer

Hi Jeff.

It looks like you have a problem with scale insects. There are different kinds of scale, but essentially, they are insects that suck the sap out of your plants. To protect themselves they have a hard shell that clamps down over them like a limpet on the beach. The black you can see is sooty mould which grows on the honeydew the scale insects secrete. A heavy scale infestation can kill the plant, so it is a good idea to get on top of it.

You can try gently scrubbing off the insects if there aren’t too many. Or spray the plant thoroughly with a good quality horticultural oil. This will coat the scale and their eggs and suffocate them and should take care of the sooty mould and the scale and your plant should recover well.

Cheers Sarah