Cause Blumeriella jaapii (formerly Coccomyces hiemalis), a fungus.
The disease is particularly severe on sour cherries, but also attacks sweet cherries in western Oregon and Washington. It has been found infrequently in arid areas east of the Cascade Range. It is especially a problem in newly planted orchards that are not being managed for brown rot. Resulting losses of fruit yield and quality are associated with a weakening of the tree as a result of early summer defoliation. Early defoliation delays flower bud acclimation to low temperatures in winter, which results in decreased flower bloom and fruit set for 2 years.
The fungus overwinters on fallen infected cherry 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 and choke cherry and plum.
Symptoms On sour cherry leaves, variously colored spots develop on the upper surface. The spot or lesion rapidly enlarges, becoming brown or purple, and dies from the center outward. Infected spots are irregular or round and occur over the entire leaf surface. Individual spots never become large. They merge together to kill large areas of the leaf. Spot development precedes yellowing and leaf dropping. The area adjacent to the spot may remain green while the rest of the leaf turns yellow (the "green island" effect). Diseased leaf tissue may separate from healthy tissue, drop out, and give the leaf a shothole appearance.
On sweet cherry leaves, spots often are larger and nearly circular. Cream-colored fungal spore masses (acervulii) appear on the lower leaf surface associated with the spots on both sweet and sour cherries. On fruit stems, infections sometimes girdle the stem to cause a fruit drop. While infections occur on the fruit, they are less common than on foliage.
- Rake up and destroy infected leaves. Leaves may be composted if completely decayed before spring.
- Make use of any practice that encourages decomposition of 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 a fungicide at petal fall, shuck fall, and 2 weeks later. Postharvest applications are helpful in wet years. Rotate or tank-mix materials from different groups with different modes of action to prevent resistant strains from developing. Limit applications from any particular group to two (2) or fewer per year. Fungi resistant to Group 3 and 7 fungicides have been detected in Michigan. Selection of products for rotation and/or mixing must consider group 7 fungicides when used through the irrigation as a nematicide. A forecasting program is available from Michigan to help time applications. Tests in western Oregon show the program is useful at higher temperatures.
- Bonide Captan 50 WP may be used in home gardens at 1 to 1.5 Tbsp/gal water. H
- Bravo Weather Stik at 3 to 4.1 pints/A. Do not apply after shuck split but may be used after harvest. Generally excellent control. Group M5 fungicide. 12-hr reentry.
- Captan 80 WDG at 1.9 to 2.5 lb/A. Applications may be made day of harvest. Generally good control. Group M4 fungicide. 24-hr reentry.
- CaptEvate 68 WDG at 3.75 lb/A. Can be used day of harvest. Group 17 + M4 fungicide. 24-hr reentry.
- Cueva at 0.5 to 2 gal/A. May be used on day of harvest. Group M1 fungicide. 4-hr reentry. O
- Eagle 20 EW at 2 to 3 fl oz/100 gal water for home orchards or landscape use. Can be applied up to the day of harvest. Group 3 fungicide. 24-hr reentry.
- Echo 720 at 3.1 to 4.1 pints/A. Do not apply after shuck split. Group M5 fungicide. 12-hr reentry.
- Flint Extra at 2.5 to 3.8 oz/A. Do not apply within 1 day of harvest. 'Concord' grapes may be injured if accidentally sprayed. Group 11 fungicide. 12-hr reentry.
- Indar 2F at 6 fl oz/A plus a wetting agent. Generally good control. Group 3 fungicide. 12-hr reentry.
- Luna Sensation at 5 to 7.6 fl oz/A. Do not use within 1 day of harvest. Do not use if already used for brown rot. Group 7 + 11 fungicide. 12-hr reentry.
- Merivon at 4 to 6.7 fl oz/A. Do not use with EC or oil-based products. Only nonionic surfactants can be used within 14 days of harvest. May be used day of harvest. Do not use if already used for brown rot. Group 7 + 11 fungicide. 12-hr reentry.
- Ortho MAX Garden Disease Control at 3.75 teaspoons/4 gal water. H
- Pristine at 10.5 to 14.5 oz/A. Can be used day of harvest. Do not use if already used for brown rot. Group 7 + 11 fungicide. 12-hr reentry.
- Procure 480 SC at 10 to 16 fl oz/A. Do not apply within 1 day of harvest. Group 3 fungicide. 12-hr reentry.
- Propiconazole-based fungicides are registered. In the Willamette Valley, smaller, deeper green leaves have been measured on 'Royal Ann' cherry trees treated with a dilute application at 3 oz/A. Group 3 fungicides. 12-hr reentry.
- Bumper 41.8 EC at 4 fl oz/A. May be used up to and including day of harvest.
- Infuse Systemic Disease Control at 2 Tbsp/gal water. H
- PropiMax EC at 4 fl oz/A. Do not use within 10 days of harvest.
- Tilt at 4 fl oz/A. Do not mix with Syllit. May be used up to and including day of harvest.
- Quash at 4 oz/A. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
- QuiltXcel at 14 fl oz/A. May be applied the day of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
- Rally 40 WSP at 2.5 to 6 oz/A. Can be applied up to day of harvest. Has eradicant activity. Generally excellent control. Group 3 fungicide. 24-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 0.5 fl oz/gal water. Can be applied up to and including the day of harvest. Do not use more than seven (7) times per year. Group 3 fungicide. H
- Sulfur 6L (52%) at 5 gal/A. May be phytotoxic if applied at temperatures above 85°F. Generally fair control. Group M2 fungicide. 24-hr reentry. O
- Syllit FL at 1.5 to 3 pints/A plus another fungicide. Do not use within 7 days of harvest. Group U12 fungicide. 48-hr reentry.
- Tebuconazole-based products. Can be applied up to and including day of harvest. Generally good to excellent control. Group 3 fungicides.
- Orius 20 AQ at 8.6 to 17.2 oz/A. 12-hr reentry.
- Tebucon 45 DF at 4 to 8 oz/A. 5-day reentry.
- Unicorn DF at 2 to 3 lb/A. Includes sulfur in the formulation. 5-day reentry.
- Topguard at 14 fl oz/A. Do not use within 7 days of harvest. Sprayers should not be used on apples. Group 3 fungicide. 12-hr reentry.
- Topguard EQ at 6 to 8 fl oz/A. Do not use with silicone surfactants or within 7 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
- Topsin 4.5 FL at 22.5 to 30 fl oz/A. Do not apply within 1 day of harvest. This material may kill earthworms, which help decompose infected leaves. Group 1 fungicide. 2-day reentry.
- Trionic 4 SC at 10 to 16 fl oz/A. Do not apply within 1 day of harvest. Group 3 fungicide. 12-hr reentry.
- Ziram 76 DF at 5 to 6 lb/A. Do not use within 30 days of harvest. Generally fair control. Group M3 fungicide. 48-hr reentry.
Note Although effective, copper products are not recommended due to phytotoxicity to fruit.
Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Fontelis.
- Serenade ASO (Bacillus subtilis strain QST 713) at 2 to 4 quarts/A. Active ingredient is a small protein. Unknown efficacy in the PNW. 4-hr reentry. O
References Green, H., Bengtsson, M., Duval, X., Pedersen, H.L., Hockenhull, J., and Larsen, J. 2006. Influence of urea on the cherry leaf spot pathogen, Blumeriella jaapii, and on microorganisms in decomposing cherry leaves. Soil Biology and Biochemistry 38:2731-2742.
Outwater, C.A., Proffer, T.J., Rothwell, N.L., Peng, J., and Sundin, G.W. 2019. Boscalid Resistance in Blumeriella jaapii: Distribution, Effect on Field Efficacy, and Molecular Characterization. Plant Disease 103:1112-1118.