Leaf spot

Septoria, Ramularia, Cercospora, Phyllosticta and Mycosphaerella spp.

also called Fungal leaf spot, Ringspot

Brown or black spots that spread and merge in wet weather, sometimes with yellow halos. Pick off affected leaves, clear fallen ones, and water at the base.

Fungus Disfiguring Rain splashAirborne sporesSeed-borne Spreads to neighbors

What you'll see

Discrete rounded spots with a definite edge, often paler or grayish in the center and dark at the rim.
Held up to the light, older spots show tiny black pinprick fruiting bodies in the dead center.
Spots begin on the lowest, oldest leaves and climb the plant after each spell of rain.
Spots merge into large brown blotches and the leaf yellows and drops, sometimes stripping the plant from the bottom.
Stems and leaf stalks may carry elongated versions of the same lesion.

Why it happens

A large mixed group of fungi that colonize leaf tissue and produce spores in the dead spot itself. They overwinter on fallen leaves, on old stems and sometimes inside the seed coat, then start again the following spring. Rain splash lifts the spores from the debris onto the lowest leaves, which is why attacks nearly always begin at the bottom.

Wet, mild spells are the trigger; a fortnight of summer rain, or a plant standing where it is watered overhead and never quite dries, will bring a fresh flush. Congested planting and poor drainage make it worse.

Treating it

Pick off spotted leaves as they appear and bin them rather than composting them.
Clear every fallen leaf from around the plant, which removes most of the splash source.
Mulch the soil surface so rain cannot splash spore-laden soil back onto the lower leaves.
Water at the base, in the morning, and thin the plant for airflow.
On valued fruit such as blackcurrants, a copper-based fungicide applied early in the season gives partial control.

Keeping it away

Rotate affected vegetables and do not follow celery with celery or blackcurrant with blackcurrant.
Buy certified clean seed and stock, since several leaf spots travel inside seed.
Mulch and stake so leaves stay clear of wet soil.
Prune fruit bushes to an open goblet so the center dries quickly after rain.
Tidy and bin all fallen foliage in autumn instead of leaving it under the plant.

Who gets it

Blackcurrants, strawberries, celery, tomatoes, hellebores, pansies and roses all suffer their own leaf spots, as do many shrubs.

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