Mycosphaerella fragariae

Fungal Disease

Common leaf spot, caused by Mycosphaerella fragariae, is a widespread fungal disease affecting strawberry plants. Also known by several other names such as Mycosphaerella leaf spot, Ramularia leaf spot, "rust," and bird's-eye spot, it primarily affects the foliage but can cause significant damage if left untreated.

Symptoms:

• The disease begins as small, deep purple, round to irregularly shaped necrotic spots, typically appearing on the upper surface of the leaves. These spots are small, around 1-2 mm in diameter, with light tan or gray centers surrounded by purplish borders.
• On young leaves, the spots remain light brown, while on older leaves, the centers transition from tan or brown to gray or white, with the necrotic center surrounded by a reddish-purple to rusty-brown border.
• Although lesions may occur on the undersides of leaves, they are less frequent and less vivid in color.
• In cases of severe infection, the intense spotting can lead to the death of infected leaves.

Disease Confusion: Common leaf spot is often confused with other leaf diseases, including leaf blight (caused by Phomopsis obscurans), leaf blotch (caused by Gnomonia comari), and leaf scorch (caused by Diplocarpon earliana). However, the lesions from common leaf spot do not enlarge as aggressively as those from leaf blight, helping to distinguish between them.

Favorable Conditions: The disease thrives in high humidity and moderate temperatures ranging between 10°C and 27°C, making humid, cool weather particularly conducive to its spread.