Strawberry leaf blight

Strawberry leaf blight is a destructive fungal disease caused by the pathogen Paraphomopsis obscurans (formerly identified as Phomopsis obscurans). This pathogen is known to cause significant damage to strawberry plantings, especially in regions with frequent rainfall and high humidity.

The disease primarily targets the foliage of cultivated strawberries (Fragaria × ananassa). While the leaves are the most common site of infection, the fungus can also colonize petioles, runners, and peduncles, which can lead to structural weakening of the entire plant throughout the growing season.

Symptoms initially appear as small, circular, reddish-brown spots on the leaf surface. As the infection progresses, these lesions enlarge, often becoming irregular or V-shaped near leaf margins. Eventually, the centers of the spots become necrotic and light brown, frequently peppered with tiny, black fruiting bodies known as pycnidia.

Environmental conditions play a crucial role in the development and spread of Paraphomopsis obscurans. The fungus thrives in warm, wet weather. Water splashing from rain or overhead irrigation is the primary mechanism for transporting spores from infected plant debris to healthy tissue. Dense plant spacing that restricts airflow further promotes the infection.

Management strategies focus on reducing the inoculum density within the field. Key practices include:

• Sanitation: Removing and destroying old or symptomatic leaves.
• Cultural control: Ensuring proper plant spacing to improve ventilation.
• Irrigation: Avoiding overhead watering to keep foliage dry.
• Fungicides: Applying preventive treatments when environmental conditions favor disease onset.