See:
Cherry (Prunus spp.) - Leaf Spot
Cause Blumeriella jaapii (formerly Coccomyces hiemalis), a fungus. Losses due to leaf spot are associated with a weakening of the tree as a result of early summer defoliation. The fungus overwinters on fallen infected leaves and in spring produces large numbers of ascospores. Air currents and rain move spores to healthy leaves. In spring, with moisture, they initiate new infections on young leaves through stomata. Once unfolded, leaves are susceptible throughout the growing season, but susceptibility decreases with age. New lesions produce more spores, which can infect healthy foliage each time it rains in the spring. Fewer infection cycles occur in the PNW compared to Midwestern production areas such as Michigan. Other hosts include apricot, bitter cherry, chokecherry and plum.
Symptoms Variably colored spots develop on the upper surface of leaves. The spots rapidly enlarge and turn brown or purple, and affected tissue dies from the center of the lesion outward. The lesions are round or irregularly shaped and occur over the entire leaf surface. Cream-colored spore masses of the pathogen appear on the lower leaf surface beneath the spots. Individual spots never become large, but numerous spots merge together to kill large areas of the leaf. After leaf spots have developed, affected leaves turn yellow and drop from the tree. The area adjacent to a spot may remain green while the rest of the leaf turns yellow. Diseased leaf tissue may separate from healthy tissue and drop out, giving the leaf a shot hole appearance.
Cultural control
- Rake up and destroy infected leaves. Leaves may be composted if completely decayed before spring.
- Make use of any practice that encourages decomposition of fallen leaves prior to spring bud break, such as mowing or flailing.
- Apply urea to leaves after leaf fall in autumn to enhance decomposition of fallen leaves.
Chemical control Apply fungicides during bloom. Rotate or tank-mix materials from different groups with different modes of action to prevent resistant strains from developing. A forecasting program is available from Michigan to help time applications. Tests in western Oregon show the program is useful at higher temperatures.
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. For non-bearing fruit trees only. Group 3 + 11 fungicide. 12-hr reentry.
- Banner MAXX at 2 to 4 oz/100 gal water. For non-bearing fruit trees only. Group 3 fungicide. 12-hr reentry.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Broadform at 5 to 7.6 fl oz/100 gal water. For non-bearing fruit trees only. Group 7 + 11 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Treated fruit must not be eaten. Group M5 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Do not use treated fruit for food. Group 3 fungicide. 24-hr reentry.
- Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Do not use treated fruit for food. Group 3 fungicide. 24-hr reentry.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Do not use treated fruit for food. Group M3 fungicide. 24-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Thiophanate-methyl-based products. Group 1 fungicides. 12-hr reentry.
- Cleary's 3336 EG at 12 to 16 oz/100 gal water. Do not use after fruit set if applied to fruiting trees.
- OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water. Do not use treated fruit for food.
Reference Pscheidt, J.W., and Byther, R.S. 2001. Prunus Diseases p 317-325 in Diseases of Woody Ornamentals and Trees in Nurseries, R. Jones., and M. Benson (ed.). St. Paul, MN: APS Press.