The black sticky substance on the leaves of your Olive Tree John is, I am sure, sooty mould which is a mould that survives and grows on the sugary glucose which has been secreted by aphids and also scale insects and, what you will need to do is with warm soapy water wash this sticky substance off the leaves. You will also need to look closely on the under side of the leaves of your Olive and Lemon Trees to see if there are any small scale insects present. If there are scale insects present you will need to spray with an insecticide but, if you are going to use the Olive and Lemon fruits you will only be able to use a contact safer insecticide. If you have no intention of using the fruits you could use a systemic insecticide which would be far more affective. With regard to the black beetles which stay motionless on the stems and leaves these could quite easily be Black Vine Weevil adults and you will need to remove these from tree and you will also need to check your soil to see if there are any white pinkish grubs as these are the grubs of the Vine Weevil and will eat the roots of your trees. There are websites available with more detailed advice/photographs on Vine Weevil. If you feel you do have problems with Vine Weevil please email BBC Radio Lancashire again I would will give you further advice.


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