Bacterial leaf spot

Pseudomonas and Xanthomonas

also called angular leaf spot, bacterial spot

Bacterial spotting of leaves: small dark water-soaked spots, often angular and boxed in by the veins, sometimes ringed with a yellow halo.

Bacterium Serious Rain splashSeed-borneSpread on tools & hands Spreads to neighbors

What you'll see

Small dark spots look wet or greasy and water-soaked, most clearly when held up to the light.
On many hosts the spots are angular, hemmed in by the leaf veins, rather than round.
A yellow halo often rings each spot, and the dead centers may dry and drop out to leave a shot-hole.
Spots run together into larger brown-black blotches and the leaf yellows and dies.
Fruit and pods can carry sunken, scabby or greasy spots as well.

Why it happens

Bacteria in the Pseudomonas and Xanthomonas groups that enter through pores and wounds in wet weather. They arrive on infected seed or transplants and are splashed about by rain and watering.

Warm, wet, humid weather and overhead watering drive it; handling or working among wet plants spreads the bacteria fast.

Treating it

Pick off and bin spotted leaves as soon as they show, and remove badly affected plants.
Stop overhead watering and water the soil only, keeping the foliage dry.
Never work among the plants while the leaves are wet.
Improve airflow by thinning and spacing so the leaves dry quickly.
A copper-based spray can check its spread, but bacterial spots cannot be cured once formed.

Keeping it away

Sow fresh, clean, certified seed and buy healthy transplants.
Rotate crops and clear away all infected debris at the end of the season.
Water at the base in the morning so any splashed foliage dries fast.
Space plants for good airflow and avoid overcrowding under cover.
Disinfect tools and wash your hands after handling infected plants.

Who gets it

A wide range of plants — tomatoes, peppers, beans, cucurbits, brassicas and many ornamentals such as delphinium and prunus.