29+ Basil Stems Turning Brown. Another disease that causes a basil plant to start turning brown is fusarium wilt, which is a mold caused by fungal infection. It causes leaves to wilt, turn yellow and fall off, and the stems to become twisted, stunted and get brown spots or streaks.
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.the next day it was all black and brown? You would see blackening of the stems, wilting, white mold, and. The spots on the leaves then progress to cover a larger surface area. The roots are probably strangling each other.