On 10 Jun, 17:31, Frank Booth Snr wrote:
Seen on underside of plant with 1 or 2 leaves similarly affected.
Otherwise growing well and looks healthy.
Any ideas what caused this?
http://tinyurl.com/2svgy4

Pretty patterns isn't it. It is rust and comes in many shapes and
forms. Look onto the link below which gives you the causes of it and
how to deal with it. I'll get rid of the whole plant (burn it) before
the leaves go yellow. Once the spores have been released you can't
tell which plants have it until it's too late. I once spent 3 days
trying to save hundreds of bellis in a garden centre from rust by
removing the affected leaves. I truly beleived I could - but in the
end I couldn't. Good luck.

http://pubs.caes.uga.edu/caespubs/pubcd/C863.htm