Experts and BHG readers answer.
Black spots growing on herbs- basil and oregano
Black spots on the upper leaves of your basil plants could be caused by a fungus, feeding from insects, or could be a response to adverse environmental conditions. If only the upper leaves are affected, I'd suggest trimming them off and watching the plants closely to see if the problem redevelops. Basil responds well to trimming, and likely will grow back thicker and leafier than ever.