Pasmo

Pasmo, caused by the fungus Mycosphaerella linicola (anamorph Septoria linicola), is a devastating disease affecting both fiber flax and linseed. It is considered one of the most serious pathological threats to flax production globally, impacting every stage of plant development from seedling to maturity.

The primary symptoms of Pasmo appear as distinct brown or dark-colored spots on leaves and stems. As the infection progresses, these spots often expand into bands, turning the stems into a characteristic mottled brown and green pattern. In late stages, small black fruiting bodies called pycnidia become visible on the stems and leaves, signaling the active production of spores.

The disease thrives in warm, humid environmental conditions. Rain splashing and wind are the primary vectors for spore dispersal, carrying the fungus from infected debris to healthy plant tissue. The pathogen can survive for several years in soil on infested crop residues, making long-term field management critical for preventing initial infections.

The economic impact of Pasmo is significant, as the infection severely compromises the quality and quantity of both fiber and seed. Plants infected with Pasmo exhibit reduced seed weight, lower oil content, and weakened fiber strength due to the premature death of the foliage and stem decay. Severe outbreaks can result in substantial yield losses, sometimes reaching 50% or more under favorable disease conditions.

Effective management requires an integrated approach to minimize the disease pressure in the field. This includes planting certified, disease-free seeds and applying appropriate fungicide seed treatments. Implementing a long rotation cycle of at least 4 to 5 years without host crops is essential to break the pathogen's life cycle. Additionally, managing volunteer flax plants and using foliar fungicides during the growing season are key strategies to safeguard high-quality yields.