Hello,

Here is some information that will hopefully help your situation:

Cherry leaf spot Blumeriella jaapii

Hosts

Tart cherry, sweet cherry

Time of concern

Late bloom through post-harvest

Damage, symptoms, disease cycle Circular purple lesions that produce white spore masses indicate leaves are infected with leaf spot. Infected leaves turn yellow and drop prematurely. Significant infections early in the season can cause premature defoliation of entire trees resulting in yield reduction, a greater susceptibility to winter injury, tree health decline, and premature tree death.

Cherry leaf spot is a fungal disease that infects leaves primarily on tart cherries and to a lesser extent on sweet cherries. The fungus overwinters on dropped leaves that were infected in the previous season. In the spring, the fungus forms fruiting bodies (apothecia) on infected leaves from the previous season that reside on the orchard floor. Ascospores, the life stage that infects leaf tissue, are released from asci on the apothecia during rainy periods. Ascospores that land on susceptible leaves germinate and infect through breathing pores or stomates on the leaves. Circular purple lesions appear where successful infection occurs, and white masses of spores called conidia grow on the undersides of lesions. Rain and heavy dew spread the conidia to adjacent leaves and initiate secondary infections. This cycle continues through post-harvest until all leaves have fallen for the season.

IPM steps for beginners Preventing the onset of infection and disease progress throughout the season is key for managing cherry leaf spot. Once infection occurs, it can be very difficult to stop its spread as most fungicides will not eradicate the fungus.

►Delay the onset of infection through an effective management program in the current season to reduce inoculum load for next year’s season.

►Prune to increase airflow in the canopy, which can improve fungicide coverage on foliage as well as reduce the relative humidity in the canopy and drying time of leaves to minimize infection severity.

►Begin management programs when the first true leaves are expanded, which indicates that stomates are present, open, and susceptible to infection. Leaf susceptibility often coincides with late bloom timing.

► Look at Table 7. Fungicides for control of major diseases on fruit crops. - Stone Fruit – Cherry Leaf Spot – Page 11

Look at: Table 12. Cultural and mechanical practices for disease and insect control on stone fruit, and the time of year to conduct them. DURING FALL OR WINTER - Collect and destroy all mummified fruit beneath trees and hanging in trees. Rake and destroy old leaves of cherry trees. Cherry Leaf Spot – Page 23. 

Look at: Table 13. Spray Schedule for Control of Stone Fruit Diseases and Insects: Peach, Nectarine, Plum, and Cherry. (Just what applies to Cherry Leaf Spot) - Page 24

All these tables are at this link:

Controlling Diseases and Insects in Home Fruit Plantings, Bulletin 780 (whole).pdf (osu.edu)

►Fungicides containing the active ingredient chlorothalonil are typically used early in the season. Using chlorothalonil products is not permitted after shuck split and before harvest.

Ready for more precision

Leaf spot infections are directly dependent on temperature and the duration of wet weather events (Figure of Eisensmith and Jones 1981 table). Therefore, monitoring weather and understanding when conditions are favorable for infection to occur is critical for effective management. The key to managing leaf spot is to prevent or delay the onset of infection for as long as possible. Currently, available fungicides do not provide adequate leaf spot control after leaves are infected. These materials are protectant fungicides, meaning sprays should be applied before predicted periods of wet or humid weather that could trigger infections to prevent the onset of infection. A cherry leaf spot disease model on Enviro- weather incorporates data on the disease’s development about past and current weather conditions to determine whether a particular location has experienced a possible infection period. Using real-time data, the model assesses the severity of infection periods. This model helps growers assess the effectiveness of their management programs and decide when to apply or reapply a fungicide. Cherry Leaf Spot Enviro-weather Model Information at this link:

Cherry Leaf Spot - Cherry - MSU - Enviroweather

Also, look at The Importance of Weather for Predicting Pests at this link:

StoneFruitIPM_ImportanceofWeatherforPredictingPests4.pdf (msu.edu)

All the above information is at this link (with images):

StoneFruitIPM_Cherryleafspot10.pdf (msu.edu)

I hope this helps – Let me know if you have any other questions!