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Septoria leaf spot

Septoria is a fungal leaf spot that thrives in warm, wet weather. On tomatoes it strips leaves from the bottom up after fruit starts to set; on parsley and celery it spots leaves and stalks. The fruit is not affected.

Fungal diseases
A tomato leaf with many small grey-centred Septoria spots
A tomato leaf with many small grey-centred Septoria spots

What it looks like

Small spots, and lots of them.

  • 2 to 6 mm (1/16 to 1/4 in) across.
    Small round spots 2 to 6 mm (1/16 to 1/4 in) across.
  • Pale grey or tan centres with a dark rim.
    Grey centres Pale grey or tan centres with a dark rim.
  • Tiny black dots in the spot centres.
    Black specks Tiny black dots in the spot centres.
  • Leaves yellow and drop from the bottom.
    Yellowing leaves Leaves yellow and drop from the bottom.

How to confirm it

Use a hand lens.

  1. Black dots in centres

    The fungus's fruiting bodies confirm Septoria.

  2. No rings

    Unlike early blight, no concentric rings.

  3. After fruit set

    On tomatoes it usually appears once fruit sets.

What to do

Remove and protect.

  1. Pick spotted leaves

    Remove and bin affected leaves.

  2. Mulch

    Stop spores splashing from the soil.

  3. Water at the base

    Keep foliage dry.

  4. Clear up in autumn

    Remove all debris.

Prevent it next time

  • Rotate crops for at least a year.
  • Space plants.
  • Buy clean parsley seed.

What not to do

Do not work among wet plants; you spread the spores.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Septoria leaf spot of tomatoes, University of Maryland Extension
  2. Tomato diseases and disorders in the home garden, Penn State Extension