White leaf spot of strawberry

White leaf spot, caused by the fungus Septoria fragariae, is a common foliar disease affecting strawberry plants worldwide. This pathogen is a member of the Fungi Imperfecti group and overwinters in plant debris, surviving until the next season to produce new spores that trigger primary infections during warm and moist spring weather.

The disease primarily infects cultivated strawberries (Fragaria × ananassa), although it can also affect wild strawberry species. While it is most frequently observed on the leaves, the pathogen can spread to petioles, runners, and fruit stalks if conditions remain favorable for fungal development, potentially causing significant physiological stress to the plant.

Symptoms typically start as small, round, reddish-purple spots on the leaves. As the infection progresses, the centers of these spots turn white or ash-gray, while the margins retain a distinct reddish-brown color. Within these white centers, tiny black fruiting bodies known as pycnidia develop, which release spores that spread via rain splash or irrigation water.

The development of white leaf spot is heavily favored by prolonged periods of leaf wetness and moderate temperatures. Dense plant canopy and poor weed control contribute to higher humidity levels around the foliage, which creates an optimal microclimate for the rapid germination of fungal spores and the spread of the infection throughout the field.

The economic impact of this disease is significant, as severe infections lead to premature defoliation, reducing the plant's photosynthetic capacity and weakening its overall vigor. To manage the disease, growers should focus on sanitation, such as removing old leaves, maintaining proper plant spacing to improve airflow, and applying registered fungicides during the early spring and post-harvest periods.

• Proper field sanitation.
• Improving air circulation through thinning.
• Crop rotation to reduce inoculum.
• Timely fungicide application programs.