Septoria leaf spot

Septoria spp.

1. Identification

Septoria spp. is a group of pathogenic fungi responsible for leaf spot diseases in various agricultural crops. These diseases are characterised by necrotic lesions, generally circular, with dark pycnidia visible inside the spots. They are important pathogens in horticultural, fruit and ornamental crops.

Diseases caused by Septoria spp.:

• Apple leaf spot — Septoria malicola Peck
• Pear leaf spot — Septoria pyricola Desm.
• Tomato leaf spot — Septoria lycopersici Speg.
• Wheat leaf blotch — Septoria tritici Rob. ex Desm.
• Rose leaf spot — Septoria rosae Desm.
• Walnut leaf spot — Septoria juglandis Lib.

These species affect horticultural crops, fruit trees, ornamentals and cereals, causing significant losses.

2. Causal agent

Ascomycete fungi, order Capnodiales, family Mycosphaerellaceae, genus Septoria. They produce hyaline, filiform conidia released from pycnidia formed within leaf lesions. They are typical pathogens of humid environments and weakened foliar tissues.

3. Main hosts

• Vegetables: tomato, celery, carrot
• Fruit trees: apple, pear, walnut
• Ornamentals: roses, garden plants
• Cereals: wheat, barley
• Other susceptible dicotyledonous species

4. Symptoms

Symptoms begin as small chlorotic spots that develop into circular or irregular lesions, brown to grey in colour, often with a yellow halo. Dark pycnidia form inside the lesions and are visible to the naked eye. The disease reduces photosynthetic area, causes premature defoliation and decreases plant vigour. In crops such as tomato and cereals, disease progression can significantly compromise yield.

5. Disease cycle

Septoria spp. survives in plant debris, fallen leaves and contaminated seeds.

Dispersal:

• Conidia carried by rain
• Spread through irrigation
• Short‑distance wind dispersal
• Tools and plant‑to‑plant contact

Infection:

• Favoured by high humidity and prolonged leaf wetness
• Occurs mainly on young leaves and weakened tissues

Polycyclic cycle:

• Multiple infections throughout the season, especially under humid conditions

6. Favourable conditions

Development of Septoria spp. is favoured by humid environments, moderate temperatures, overhead irrigation and dense canopies with poor ventilation. Contaminated plant debris acts as a continuous inoculum source.

7. Disease management

Management focuses on reducing leaf moisture, improving ventilation and removing infected leaves. Crop rotation and the use of less susceptible varieties reduce disease pressure. Regular monitoring enables timely interventions. Biological control may be applied with authorised antagonists. Chemical control must follow local regulations and alternate modes of action to avoid resistance.

References

• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• EPPO – Diagnostic Protocols for Septoria spp.
• FAO – Guidelines for Integrated Disease Management in Horticultural and Field Crops.
• Jones, J.B. et al. (2014). Compendium of Tomato Diseases.