Botrytis leaf blight

Taxonomic classification and pathogen type: Botrytis squamosa belongs to the kingdom Fungi and the genus Botrytis. It is a specialized fungal pathogen that causes Botrytis leaf blight, a major foliar disease that frequently affects Allium crops worldwide.

Diseases and host crops: The primary host for this pathogen is the common onion (Allium cepa), although it can also affect leeks and shallots. The disease is characterized by small, white, necrotic spots on leaves that eventually enlarge, causing significant tissue death and reducing the plant's photosynthetic capacity.

Biology and life cycle: The pathogen survives as sclerotia in the soil or on infected plant debris from previous seasons. During cool, wet conditions in the spring, it produces conidia, which are disseminated by wind or splashing rain. Infection occurs when these spores land on leaves, germinating and penetrating the epidermis.

Environmental conditions and impact: Disease development is favored by temperatures between 15°C and 20°C and prolonged leaf wetness. The economic impact is significant, as the destruction of foliage leads to smaller bulb size, lower quality, and increased susceptibility to secondary infections that cause storage rots.

Protection and control measures: Effective management requires an integrated approach, including crop rotation of at least 3-4 years and the removal of crop residues. Fungicide applications, including protective and curative products, should be timed based on environmental conditions and disease scouting early in the growing season.

• Implementing strict crop rotation programs.
• Ensuring proper spacing for better air circulation.
• Removing volunteer onions and weeds.
• Applying fungicides during periods of high humidity.
• Harvesting onions only after the foliage has matured and dried.