Lettuce & Greens brown spots on leaves
There are 2 common causes, and they need completely different responses — so working out which one you have matters more than treating quickly.
1 of them can kill the plant. Rule those out first.
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.
The 2 causes, and how to tell them apart
1.Downy Mildew
Act nowFungal disease
Yellow patches on the upper leaf surface with straight edges, boxed in by the leaf veins so they look angular rather than round. Turn the leaf over and there is grey, purple or brown fuzz directly underneath each yellow patch.
How to know it is this one
Always check the underside. Fuzzy growth beneath a yellow patch is definitive.
2.Bacterial Leaf Spot
TreatableBacterial disease
Small dark spots that look wet or greasy, often with angular edges because they stop at the leaf veins, sometimes surrounded by a yellow halo. In humid weather the spots look water-soaked; in dry weather the centres fall out leaving small holes.
How to know it is this one
Greasy, water-soaked appearance, especially in the morning.
Still not sure?
The diagnostic key adds two more questions — which part is affected and where the trouble started — and those usually settle it.
Run the diagnostic key