Cause Septoria exotica is a fungus that is favored by conditions that keep leaves wet. Pseudophaeophleospora atkinsonii (formerly Kirramyces hebes) has been described, which has similar symptoms but larger sized leaf spots. It is not known which might occur in the PNW.
Symptoms The first symptoms are small black spots on the leaves, which enlarge and form an ash-colored center. Several dark fruiting bodies (pycnidia) may be found in the center of the spots. Individual leaves may have large numbers of these spots. The disease is particularly noticeable on large-leaved cultivars, but can be seen on smaller-leaved types as well. Lower leaves on the stem tend to fall off, which makes the plants look "leggy".
Cultural control
- In the landscape, plant in full sun and avoid overhead water unless the foliage can dry quickly and thoroughly.
- Avoid over-crowding by adjacent plants.
- Remove fallen leaves and plant debris.
Chemical control No chemicals are specifically labeled for this disease on this host. Many of the broad-spectrum fungicides may be effective and could be used if not phytotoxic.
Reference Wu, W., Sutton, B.C. and Gange, A.C. 1996. Revision of Septoria species on Hebe and Veronica and description of Kirramyces hebes sp. nov. Mycological Research 100:1207-1217.