See:
Cause The fungus Boeremia exigua var. viburni (formerly Phoma viburni) has not been formerly reported for the PNW but Phoma sp. have been found many times by the OSU Plant Clinic. Wet weather is favorable for most fungal diseases of this type.
Symptoms The main stem and side branches develop discrete, slightly sunken lesions that are light-brown on older wood to purplish-black on younger tissues. Lesion may girdle the stem resulting in wilting and death of the plant above the canker. Stem lesion are common near the ground line. Round necrotic leaf spots with a purplish margin can also occur as well as blackened shoot tip dieback. A cutting rot has also been observed.
Cultural control
- Destroy affected leaves or plant debris if practical.
- Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
Chemical control
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Daconil Weather Stik at 1.38 pints/100 gal water may be effective for fungal leaf spots. Group M5 fungicide. 12-hr reentry.
- Mancozeb-based products can be used for fungal leaf spots. 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.
- Monterey Liqui-Cop at 3 Tbsp/gal water. H
- Nu-Cop 50 DF at 1 lb/100 gal water. Use for both fungal and bacterial leaf spots. Group M1 fungicide. 48-hr reentry.
- Orkestra at 4 to 10 fl oz/100 gal. 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.
- Phyton 27 at 1.5 to 2.5 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
Reference Boerema, G.H., and Griffin, M.J. 1974. Phoma species from Viburnum. Transactions of the British Mycological Society 63:109-114.