A Mould for all Seasons

Thank for the news and advice!
I have a fairly large Kaffir Lime in a tub, never had a problem over many years, suddenly developed BLACK MOULD in/on/under the leaves. Also ants LOVE it and run all over it.
It looks very healthy apart from this.
What to do?
Many thanks, Lena

I love this one because I can talk about Aphid poo and snigger like a school boy.

I'm pretty sure that Lena's Lime has Sooty Mould.

That's a pretty disastrous infestation on oranges.  Click here to see the original and get some detailed information on the source of the mould, Mealy Bugs.

This mould is quite common on Citrus, Gardenias, Crepe Myrtle, Azaleas and I remember Oleander from childhood. Fortunately for me it is not a common problem with annual flower or vegetable seedlings.  The interesting thing is that the mould fungi does not actually grow on the plant but in the sugary Honeydew secreted by sap sucking insects: Aphids, Mealy Bugs, Scale, White Fly, etc.  Honeydew?  That's the polite term for bug poo, hence my juvenile merriment.

Of course it's unsightly and it is a clear sign that something will have to be done about the sap suckers.  I have written about sap suckers previously, just follow this link if you want all the details.

The short and honey sweet version is spray with Confidor if you are happy with chemicals.  Very effective and apparently safe Confidor is a 'systemic' insecticide so it gets into the plants system and is sucked up by the insect.
Not into chemicals? White oil is very effective and drowns the bugs on the plant's surface.  I have always been a fan of Clensel, a soap formulation that knocks down insects.  Keep an eye out for Neem preparations, I don't know any brand names but have a look at this link if you are interested.

Oh, and the ants that Lena noticed?  I think that's nature managing the aphid population.

Enough for now.  Di wants me to look at Powdery Mildew next week.  Timely of course.