Bacterial speck

Pseudomonas syringae pv. tomato

Tiny black specks with a yellow halo on tomato leaves and pinprick dots on the fruit. A cool-wet-weather disease, and mostly cosmetic on the fruit.

Bacterium Disfiguring Seed-borneRain splashSpread in waterSpread on tools & hands Spreads to neighbors

What you'll see

Very small dark brown to black spots, one to two millimeters, each ringed with a clear yellow halo.
Specks concentrated at the leaf margins and running together into dark patches there.
Tiny raised black dots on green fruit, superficial and no bigger than a pinprick.
Black flecks on stems and flower stalks, and flowers dropping in a bad case.
Damage worst on the lower leaves early in the season, easing as the weather warms.

Why it happens

A bacterium that comes in on seed and on transplants and survives on debris and on volunteer tomatoes. It moves in water — splash, overhead irrigation, and handling wet plants. It is easily confused with bacterial spot, but the specks are smaller, the halo is brighter, and the weather is different: speck likes it cool, spot likes it hot.

Cool and wet: temperatures between 15 and 20 °C with long leaf wetness. A cold wet spring after planting out is the classic setting, and it usually fades once summer heat arrives.

Treating it

Pick off the worst lower leaves and bin them, and stay out of the plants while they are wet.
Switch to base watering in the morning and mulch to stop the splash.
Space and prune to open the canopy so the leaves dry quickly.
Use fruit as normal — the specks are skin-deep and the tomato underneath is fine.
A copper spray protects new growth in a prolonged cold wet spell but does nothing for what is already spotted.

Keeping it away

Buy or hot-water-treat seed, and do not save seed from an affected plant.
Raise your own transplants and inspect bought ones at the lower leaves.
Rotate tomatoes and remove volunteers and solanaceous weeds.
Plant out after the cold wet weather has passed rather than at the earliest possible date.
Grow resistant cultivars where they are available; the Pto gene gives real resistance to the common race.

Who gets it

Tomatoes chiefly, and occasionally peppers and related weeds.