Looks like mint rust. Thin out affected sections and disgard in the trash. Thin remaining stand for good air circulation. Water only the roots and not the leaves. Spray the remaing stand and surrounding area with good quality organic neem oil,
as directed according to the label for rust prevention for new growth. More is not better and may do more harm than good always follow label instructions.
Mint will resprout from their roots. So really no need to start over just to have new plant develop rust also... try and get the rust under control with the roots you already have and prune new growth for good air flow.
It's not a disease persay... it's caused by a common fungus (puccinia menthae). Some people just say disease. But it's root cause is a common fungus. Puccinia menthae can be identified by orange, yellow, and black spots on the leaves, as well as distortion of new growth shoots. Puccinia menthae affects mint, marjoram, and savory.
I can't really tell but it looks like it's setting deep in a wooden basket. If so that's a good environment for fungus development.
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