Pasmo disease of flax

Pasmo disease of flax is a significant fungal infection caused by the pathogen Discosphaerina fulvida (formerly Septoria linicola). It is one of the most destructive diseases affecting flax worldwide, causing premature defoliation, stem lodging, and a reduction in both fiber quality and oil seed yield.

The pathogen is a fungus that produces pycnidia and perithecia as primary reproductive structures. The disease cycle is largely driven by infected crop debris left in the field from previous harvests, which serves as a primary inoculum source. Seed transmission also plays a crucial role in the initial introduction of the fungus to new fields.

Symptoms typically begin as small, circular, brown to black spots on the leaves and cotyledons. As the infection progresses, these lesions merge into irregular, dark-colored bands that encircle the stem, a classic sign of the disease known as "pasmo" (which translates to "stripes" or "bands"). Affected stems become brittle and may break prematurely under stress.

The development of the disease is highly dependent on environmental conditions, particularly moisture. Warm, humid weather with frequent rainfall creates the ideal environment for the release and dissemination of spores. Dense plant populations increase canopy humidity, further exacerbating the spread of the pathogen during the mid-to-late growth stages of the flax plant.

Effective management requires an integrated approach to break the disease cycle. Key strategies include:

• Planting resistant or tolerant flax varieties.
• Using certified, fungicide-treated seeds.
• Implementing a robust crop rotation with a gap of at least 3 to 4 years between flax crops.
• Managing crop residues through deep tillage to promote decomposition.
• Applying foliar fungicides when conditions are conducive to disease outbreaks.