Healthy basil plant leaves turn dark and die
Leaves on my beautiful thriving basil plant suddenly-almost overnight-darkened and died. Even the plants from cuttings that I rooted in water and then planted were beautiful and then turned dark and shriveled. I've been growing basil for 60 years and have never seen this happen. Thank you in advance for hopefully providing an answer. Mickey Bezjak
Certified GKH Gardening Expert
This is most likely Bacterial Leaf Spot.
Damp growing conditions and lack of air circulation can be contributing factors. Keeping water from splashing unto the leaves can help.
Here is a link that explains this issue.