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Rhododendron looking very poorly

We have a 40 year old plus Rhododendron which this year is looking very sorry for itself. Less leaves have formed and what leaves there are, are drooping and have a coating of a "black soot". The flower buds are poorly formed and dropping before opening. We have given it a feed of a Miracle Grow specialist rhododendron feed and are watering each night . Any ideas would be most welcome as we would hate to lose this matriarch of a tree from the garden.

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  • ObelixxObelixx Vendée, Western FrancePosts: 22,270
    The black stuff looks like sooty mould which grows on the sugary excretions of insects such as aphids or scale insects.

    You need to clean it off each leaf so they can photosynthesise and feed the plant.  A soft damp cloth should be enough but I'd give a good spray form a hosepipe first to loosen and dampen it.  You don't need chemicals, just patience, lukewarm water and a damp sponge will do.

    Then you need to check for the source.   At this time of year any aphids will swiftly be hoovered up by tits and sparrow to feed their young in the nest and ladybirds and hoverfly will clean up the rest.  If it's scale insect, you can wipe them off with a sponge or cotton pad soaked in alcohol.

    See here for more info - https://www.rhs.org.uk/advice/profile?pid=770 
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
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