Leptotrochila leaf spot of onion

The disease is caused by the ascomycete fungus Leptotrochila porri. This pathogen is specifically known to affect members of the Allium genus, functioning as a parasite that targets leaf tissues and interferes with the vital physiological processes of the host plants.

This fungus primarily impacts Allium species, with onion (Allium cepa) and leek (Allium porrum) being the most susceptible crops. By invading the leaf epidermis and mesophyll, the pathogen causes chlorosis and eventual necrosis, which significantly compromises the health and growth potential of the entire plant.

Symptoms of the infection include the development of elongated, light-colored spots that often exhibit a distinct dark margin. As the disease progresses under humid conditions, the centers of these spots may become covered with small, reproductive fungal structures, causing the tips of the leaves to wither and die prematurely.

The development and spread of Leptotrochila porri are heavily influenced by cool, wet weather patterns. Moisture is essential for spore germination and infection, while wind and rain splashes facilitate the dispersal of spores throughout the field, making dense plantings particularly vulnerable to outbreaks.

To effectively manage the disease and prevent significant yield losses, growers should adopt an integrated pest management strategy:

• practicing long-term crop rotation to break the pathogen's life cycle;
• removing and destroying crop debris to reduce initial inoculum levels;
• maintaining proper plant spacing to improve air circulation and reduce humidity;
• applying registered fungicides during periods of high disease pressure.