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Cause Several fungi and bacteria have been reported in other regions and may be important in the Pacific Northwest. Phyllosticta sp., Phoma sp. and Cercospora sp. have been found in Oregon. Spot anthracnose caused by Sphaceloma viburni has been reported from Washington. Pseudomonas syringae pv. viburni also causes a leaf and stem spot.
Symptoms Cercospora leaf spot is characterized initially by the development of small dark-red-to-purple leaf spots. Spots become angular being bounded by major leaf veins. The center of spots become lighter-brown-to-tan with dark-purple borders.
Spot Anthracnose - Small, mostly circular leaf spots with a gray-to-white center and brown margin. Spots may be circular to triangular to irregular shaped. Black acervuli may be seen within the leaf spots. Spots can be numerous or scattered on a leaf and often follow leaf veins.
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 Best used before symptoms develop. Bacteria resistant to copper products have been detected in many nurseries. Most of these products are fungicides for fungal leaf spots but group M1 fungicides can be used on both organisms.
- 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 Jenkins, A.E., Bitancourt, A.A., and Pollack, F.G. 1946. Spot anthracnoses in the Pacific Coast States. Journal of the Washington Academy of Sciences 36:416-421.