Plant Pathology: Extension: Plant Disease Library

Septoria

Important diseases: Leaf spots on numerous plants, Purple leaf blotch.

Septoria causes numerous leaf spot diseases on a wide variety of vegetables, field crops, forages, and ornamentals. It also causes blights and blotches.

In general, leaf spots tend to be small, round, with white to light tan or gray centers and a purple or brown border or a zone of yellow tissue.

Some spots may be tan to brown and grow together to cause blotches.

Leaf spot symptoms vary with each host. In general, leaf spots tend to be small, round, with white to light tan or gray centers and a purple or brown border or a zone of yellow tissue. Some spots may be tan to brown and grow together to cause blotches. On dogwood, leaf spots tend to be angular with dark purple margins. Small black pimple-like fruiting structures (pycnidia) are produced within leaf spots.

Pycnidia are dark, separate, globe-shaped with an ostiole (opening at the apex) from which conidia are extruded, and erupt through the surface of the infected plant tissue.

Conidia (spores) are produced within pycnidia (fruiting structures). Pycnidia are dark, separate, globe-shaped with an ostiole (opening at the apex) from which conidia are extruded, and erupt through the surface of the infected plant tissue.

Conidia are produced on short conidiophores. They are clear, narrowly elongated to filiform, and several-celled. Septoria conidia may be confused with Cercospora conidia when seen alone. However, Cercospora conidia are produced on open condiophores whereas Septoria conidia are produced within pycnidia.