Cause Phyllosticta sp. and Dothiorella candollei (formerly Macrophoma candollei), fungi, have been found infrequently by OSU's Plant Clinic. The fungi survive on dead leaves under the shrub.
Symptoms Leaves show discolored spots, which sometimes are filled with small, black, fruiting bodies (pycnidia), dotting the lesion surface. Some leaves may be heavily infected, others have only a spot or two.
Cultural control
- Cut out all dead branches.
- Remove dead leaves from crotch areas inside the canopy.
- Space and prune (thin) plants for good air circulation. Thinning is best done in the fall during dry weather using sharp bypass pruners.
- Grow plants in well-drained media or soil with a pH between 6.8 and 7.5. Light shade of 20% can also reduce injury from summer and winter extremes.
Chemical control Spray with fungicides starting just before new growth starts in spring.
- Bordeaux 4-4-50. O
- CuPRO 5000 at 1.5 to 5 lb/A but only up to 2 lb/A when new growth is present. Group M1 fungicide. 48-hr reentry.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- Orkestra at 8 to 10 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Pageant at 8 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
Reference Liu, Q., Yu, J., Hu, Y., Yan, J., Cheng, H., and Qi, X. 2009. Phyllosticta sp. nov., a New Pathogenic Species from Buxus sincia. Journal of phytopathology 157:470-473.