Onion anthracnose

The causative agent of the disease is the imperfect fungus Colletotrichum circinans, which causes a dangerous disease known as onion anthracnose. This pathogen mainly affects bulbous crops during the growing season and during subsequent storage. The fungus persists in the soil and on infected plant debris, forming microsclerotia that can remain viable for several years.

The main crops susceptible to infection are bulb onions, shallots, and leeks. Varieties with white scales are particularly sensitive to the infection, as they contain fewer phenolic compounds that inhibit pathogen penetration compared to colored varieties.

Symptoms of the infection appear as small dark spots on the outer scales of the bulbs, which eventually merge into concentric circles. Under high humidity, the cushions of the fungus's conidial sporulation form on these areas, colored black. On the leaves, the disease manifests as elongated sunken spots, leading to premature drying of the plant's aerial part.

The development of the pathogen is favored by high air humidity (above 80%) and moderately warm temperatures in the range of 20–25°C. The spread of the infection occurs through conidia carried by raindrops, irrigation water, as well as through tools and infected planting material. The fungus develops particularly actively in dense plantings with poor ventilation.

The damage caused by anthracnose includes a sharp decrease in product marketability and significant losses during storage due to the development of secondary bacterial rots. To protect plants, it is recommended to practice crop rotation (returning to the same field no earlier than 3-4 years later), use healthy planting material, and ensure timely removal and destruction of plant debris. If necessary, preventative fungicides are used.