Could be "rust", a fungal infection. I'd cut it back hard to remove all affected growth and take off the top layer of compost (if it's pot grown) where spores may be lurking. Top it up with fresh compost. I've found chocolate mint quite a resilient plant, and cuttings strike very easily in water if you have any unaffected stems. Hope yours bounces back 😊
it seems to be all the lower leaves the top new growth is all ok . will it carry on and spread to my other mints which are all in pots as they are next to each other. but thankyou for your answers 😀
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I'd cut it back hard to remove all affected growth and take off the top layer of compost (if it's pot grown) where spores may be lurking. Top it up with fresh compost. I've found chocolate mint quite a resilient plant, and cuttings strike very easily in water if you have any unaffected stems.
Hope yours bounces back 😊
RHS info in the link below.
https://www.rhs.org.uk/advice/profile?PID=220