I have three potted sweet Basil plants in my backyard. Two of them look great, but the middle one is a lighter green color and has browning and curling leaves. I live in zone 6. I grew them from seed. They're in a partly sunny location. I water when they're dry and fertilize with Miracle Grow periodically. We've had a spell of cooler weather (3 weeks or so) and that seems to be about when it started. Any ideas? I'm a bit at a loss since the other two plants look fine.
Mildew due to over watering- and keep the area underneath the plants clean of dead leaves- this will encourage other problems in too if not treated. pick off affected leaves or even remove affected plants completely. there also seems to be a slight touch of scorch on the leaves and possible slug damage due to dead leaves encouraging them in- overly wet conditions?
I would try will less fertilizer (and changing the soil). The soil seems very rich (too much), so i think roots could have some mushroom problems.
Looks like herbicide damage. Any chance the soil in that pot came from a different source ?