The leaves started discoloring and becoming crisp. I've been plucking off the bad looking leaves. Today I came home to find an explosion of black dots all over the plant. Does this mint have a fungal infection? (see pix below)
It is being eaten by moth or butterfly caterpillars. The black dots are 'frass' (caterpillar turds). Inspect the leaves carefully, and remove all the caterpillars you find (there may be several). Pay particular attention to any leaves that are folded over and stuck together with webbing. If you can't find them in the leaves, check on the soil or under the pot, or look at night; some caterpillars hide during the day and emerge to feed at night.
Thank you! I never knew there could be an explosion of caterpillar turds like that :) I examined the plant very closely before I posted the question, and so was surprised when you said it was caterpillars because I was so sure I got nothing. But yesterday I finally found one green caterpillar squirming away. Hope now the plant can recover.
Last year caterpillars completely ate my mint (started from seed earlier in the season) when I was away for ONE day. Happy to report the potted mint is back with gusto this year. You'll have try harder than that to kill mint. Good luck!