The mint plants grown in pots has some white mold type deposits on the leaf. See picture below. Does anyone know what it is?
That looks just like powdery mildew that we had on our spearmint. I would pronounce it powdery mildew. You could treat it. I hear milk works great for the purpose. There are probably a lot of sites that explain how to treat it. Another solution might be better with mint, though.