Cherry leaf spot

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Conidia of cherry leaf spot

Cherry Leaf Spot is a fungal disease that affects cherry trees, including both sweet (Prunus avium) and sour (Prunus cerasus) varieties. The disease is caused by the fungus Blumeriella jaapii (formerly known as Coccomyces hiemalis). Cherry leaf spot is primarily a concern in regions with wet spring weather, as the fungus thrives in these conditions. The disease can significantly impact cherry production by causing defoliation, weakening trees, and reducing fruit yield and quality.

Symptoms

The first signs of cherry leaf spot usually appear on the upper surfaces of the leaves as small, purple spots. As the disease progresses, these spots enlarge and turn brown, with a white or gray center where the fungal spores are produced. The infected leaves may eventually yellow and fall off the tree prematurely, a condition known as defoliation. Severe infections can lead to significant leaf loss, which weakens the tree by reducing its ability to photosynthesize and store energy for the following year's growth and fruit production.

Lifecycle

Blumeriella jaapii overwinters in fallen leaves from the previous season. In spring, the fungus produces spores (ascospores) that are dispersed by wind and rain to infect new leaves. Secondary infections can occur throughout the growing season as the fungus produces another type of spore (conidia) on the infected leaves, which also spread to new leaves. The disease cycle continues as long as conditions are favorable, with multiple infection cycles possible in a single growing season.

Management

Management of cherry leaf spot focuses on cultural practices, chemical control, and resistant varieties:

• Cultural Practices: Sanitation is crucial for managing cherry leaf spot. Removing and destroying fallen leaves can reduce the number of fungal spores available to start the infection cycle in the spring. Proper pruning to improve air circulation within the canopy helps leaves dry more quickly, reducing the duration of leaf wetness that favors fungal growth.

• Chemical Control: Fungicides are often used to protect trees during susceptible periods, especially in commercial orchards. Applications may begin at bud break and continue at regular intervals until the end of the wet season. It is important to follow label instructions and rotate fungicides to prevent the development of resistance.

• Resistant Varieties: Breeding efforts have produced cherry varieties with varying levels of resistance to cherry leaf spot. Planting resistant varieties can reduce the reliance on fungicides and other management practices.

Economic Impact

Cherry leaf spot can have a significant economic impact on cherry producers. The cost of fungicide applications, potential yield losses, and the labor involved in cultural management practices all contribute to the economic burden of the disease. Additionally, severe defoliation can affect the quality and quantity of fruit in the following year, further impacting profitability.