Cause Alternaria alternata, Pestalotia sp., and Phyllosticta sp. have been found by the OSU Plant Clinic. Many leaf-spotting fungi overwinter in diseased leaves and are favored by wet weather. Alternaria gains entry to leaves through wounds.
Symptoms Circular to angular necrotic spots on leaves.
Alternaria spots are reddish, circular or with an irregular margin and a tan center; sometimes faintly zonate. Smaller spots can coalesce into larger spots. Some spots may show a chlorotic halo around the necrotic area.
Cultural control
- Maintain adequate fertility.
- Avoid overhead irrigation.
- Remove fallen leaves from propagation area.
Chemical control
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Chipco 26019 FLO at 1 to 2.5 quarts/100 gal water. Group 2 fungicide. 12-hr reentry.
- CuPRO 5000 at 1.5 to 2 lb/A. Group M1 fungicide. 48-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Group M3 fungicide. 24-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Trinity at 4 to 12 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Hartmann, G.C. 1961. Alternaria leaf spot of Pieris japonica. Plant Disease Rep, 45:938-939.