Bacterial Leaf Spot
TreatableBacterial disease · spreads to other plants · also called bacterial speck
Bacterial spots are distinguished from fungal ones by looking water-soaked and by having angular rather than round edges, because bacteria spread through the leaf's plumbing and get stopped by veins. They spread explosively in warm wet weather and on hands and tools moving among wet plants.
What it looks like
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 confirm it
- Greasy, water-soaked appearance, especially in the morning.
- Angular edges bounded by the leaf veins rather than neat circles.
- Yellow halo around individual spots.
- Centres may drop out, leaving a shot-hole appearance.
What to do
- 1Remove affected leaves and bin them.
- 2Never work among wet plants — this is the single biggest factor in how far it spreads.
- 3Copper sprays slow it but will not cure it.
- 4Space and prune for fast drying.
What it gets confused with
One observation settles each of these.
Septoria spots have pale grey centres with tiny black dots and are round. Bacterial spots are darker, angular and greasy.
Early blight has concentric rings; bacterial spots do not.
Preventing it next time
- Use certified disease-free seed; these bacteria are frequently seed-borne.
- Rotate out of the family for two years and clear debris.
- Water at the base, in the morning.
Plants affected
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.