"Geoff" wrote
Our soil tends to be alkaline and we have four camelias in one bed which
have only been there five years and have been OK up to this year. I will
not describe what awful stuff was buried beneath where they are planted,
but suffice to say the previous owners had three bloody big dogs which
never went walkies!!

One camelia did not flower this year although the other three put on a
brave show but now something nasty seems to be attacking all them.

Many of the leaves of one plant are covered with what looks like soot and
on some of its leaves the soot has brown circular patches about 4-6 mm in
diametre.

Can anybody diagnose the problem and perhaps give an effective remedy
please.

Black soot is Sooty Mould which is growing on Honeydew secreted by sap
sucking insects. Being Camellias it will be Scale Insect, look under leaves
and on young wood for brown scales which do rub off. There are sprays
available to treat this pest but unfortunately it is common on Camellias,
often there is a tree locally that is permanent host, so it will be an
ongoing battle.
Have you watered the plants with their annual Sequestered Iron yet this
year?

--
Regards
Bob Hobden
17mls W. of London.UK