Why has my mint plant gone yellow?

Question

I`ve been growing some mint in a container (with holes) it`s been doing very well until the last fort- night . It`s now going yellow and has some white powdery marks on it , what has happened ?

Answer 1

I'm inclined to think that you have a fungus on the leaves.  Prune all the diseased stems off and see if there is any improvement.

Answer 2

If it is all yellow there could be a problem with the Ph or minerals in the soil, or too much water.  Just the lower leaves yellowing, its just that they are shaded by the up leaves, or its too dry and it is letting the lower ones die off to save the newer ones.  

The white powder is a fungus.  That makes me think the leaves staying too wet.  Mint usually like moisture but too much can cause problems, lilke what you've described here.