[3] Cherry leaf spot is caused by the ascomycete fungus Blumeriella jaapii (formerly known as Coccomyces hiemalis; anamorph Phloeosporella padi).

Ascospores are produced in these fungal fruiting bodies and are forcibly ejected during rainy periods for about 6–8 weeks, starting at petal fall.

Infected leaves are filled with numerous black lesions that cover an obvious portion of the leaf.

Leaves with lesions present typically fall off early in the growing season and it is common for seriously affected trees to be defoliated by midsummer.

If the disease is not controlled and allowed to persist for several years there could be various adverse effects to the overall cherry production of a tree primarily due to the cycle of early season and repeated defoliation.

This fruit will typically remain light colored, soft, and very low in soluble solids and sugar.

In early spring (at the time of petal fall), fungal fruiting bodies called apothecia develop in these leaves.

The ascospores can stick to the leaf and, given a film of water and optimal temperature, germinate within hours of adhesion.

Because the ascospores are produced through sexual reproduction, this part of the life cycle can also introduce genetic variation that may be important, for example, in the evolution of fungicide resistance.

These conidia are horn-shaped and have hydrophilic outer cell walls that make them easily miscible in water.

When selecting a site for an orchard, use areas that have well drained soils, much sunlight, and good air circulation.

[13] Leaf litter removal is not very practical for large commercial growers due labor needs and number of trees but if at all possible, a majority of the old leaves should try to be collected.

When planting, growers should select locations which have a large amount of direct sunlight such as a south facing slope.

Proper pruning should also be completed to increase the amount of sunlight penetration and air circulation through the canopy.

Prior to shuck split, the recommended fungicide for cherry leaf spot is chlorothalonil (Bravo and generics).

At least two applications of chlorothalonil should be made before shuck split with the goal to minimize the potential of infection at this early stage.

Fungicides are much more effective when applied early in the season when the inoculum load is low as cherry leaf spot is a prolific, unrelenting, tireless disease.

[14] This was particularly surprising because the weather conditions were not notably conductive to the super development of cherry leaf spot infection.

These early and significantly strong infection rates indicate that the fungus is evolving and becoming resistant to certain fungicide treatments.

George Sundin, a professor and fruit extension specialist from Michigan State University advocates that the new chemistries of succinate dehydrogenase inhibitors (SDHIs) are also effective in controlling cherry leaf spot.

[15][16] Sterol demethylation inhibitor (DMI) fungicides including fenarimol, fenbuconazole, myclobutanil, and tebuconazole were used immensely in the 1980s and 1990s.

It has been scientifically proven that the standard application of copper based fungicides does not have any adverse effects on the developing fruit.

[22] Additional research conducted in the 1940s demonstrated that it was absolutely necessary to monitor and control leaf spot through preventative sprays and measures.

These experiments showed that poor control of the pathogen resulted in a 72 percent loss of tree branches for the growers who did not spray.

Growers who used fungicides regularly and persistently commonly suffered no or very little loss from cherry leaf spot each year.