Thank you both for your replies.
The plant shows no sign of dehydration and is otherwise a healthy plant and flowered recently.
Of course I find that if I look hard enough at any orchid I find some blemishes on leaves that cannot be explained.
I will get some of the cleary's fungicide and drench the roots just to be on the safe side. However if this is the fusarium ring then the fungicide may do no good as advice says to keep cutting until no ring is detected and then drench. However, I do not want to cut my plant up if this is not the fusarium ring.