Septoria Leaf Spot

What is it?

Septoria fungi infect leaves (and sometimes stems), producing distinctive small spots with grey/tan centres dotted with tiny black fruiting bodies. They survive in debris and seed and spread by splash, favouring prolonged leaf wetness.

How to identify it

• Numerous small (2-5 mm) circular spots with pale tan/grey centres and darker margins.
• Tiny black pycnidia (fruiting bodies) speckling the spot centres — diagnostic under a hand lens.
• Lower, older leaves affected first, yellowing and dropping as the disease moves upward.
• Heavy defoliation exposing fruit to sunscald in severe cases.

Life cycle & spread

Survives in crop debris and on seed; spores spread by rain splash and overhead irrigation to lower leaves, then progress up the canopy in repeated wet cycles.

Conditions that favour it

Warm, wet, humid weather; prolonged leaf wetness; dense canopies and splashing irrigation; carry-over inoculum in debris.

Damage and how it spreads

Progressive defoliation reduces photosynthesis and yield, weakens plants and exposes fruit to sunscald; in cereals, leaf blotch cuts grain fill.

Monitoring & scouting

Scout lower leaves in warm wet spells; confirm with a hand lens (look for black pycnidia in spots); act preventively as conditions favour disease.

How to control it

1. Improve airflow, avoid overhead wetting, remove debris and rotate;
2. apply protectant programs preventively and at first symptoms, starting low in the canopy.

Preventing it next season

Airflow/canopy management, drip vs overhead irrigation, debris removal, rotation and clean seed, plus preventive sprays in wet periods.

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