Septoria under the radar

Septoria disease caused by Septoria linicola is a fungal disease of flax that is mainly observed in France. The disease is mainly observed on winter flax, however with the multiplication of flax cultivated areas in the Interreg region, the disease is also making its way to Belgium. In case of high disease pressure, a yield loss can reach up to 70%.

The first symptoms can be recognized by circular brown spot on the basal leaves, which spread from the bottom to the top of plants. Then some characteristics symptoms with alternating yellow-brown stripes can be observed on the stem, followed by an early senescence of plants. The disease occurs mainly in wet and humid weather. Whereas in 2025 little to no symptoms have been observed due to the drought, this year the disease was slightly more present. The wetter month of February may have played a role in this. As part of the Trans-Pathoflax 2.0 project, an information sheet was produced presenting symptoms, conditions and possible control measures.

After the exceptionally wet growing season of 2024, the persistent drought of 2025 and 2026 is presenting a new challenge for flax cultivation. Winter flax is currently retting, while spring flax is being pulled on a large scale. In some areas, the flax has suffered considerably from the thunderstorms in June. Hopefully, further severe thunderstorms and extreme weather conditions will remain absent this summer, allowing the retting process to proceed under favourable conditions.

As part of the Trans-Pathoflax 2.0 project, several trial fields were established this year in Flanders (Inagro) and France (Arvalis) to monitor the impact of three major fungal diseases on flax. The effect of the drought on the occurrence of these diseases this season remains uncertain.

Verticillium wilt

More than 20 flax varieties were sown on a on a plot where natural inoculum of Verticillium dahliae was present, to observe their response.
Additionally, a second trial was set up on the same plot to evaluate the effect of various biocontrol agents on flax growth and disease pressure.

Septoria & Powdery Mildew

Around 20 varieties are being monitored for their susceptibility to Septoria and powdery mildew.
The effectiveness of various biocontrol products – including two developed within the partner project Trans-Lipo – is also being investigated.

IPM approach to powdery mildew

Two fibre flax varieties (tolerant vs. susceptible) are grown side by side in combination with a biocontrol agent to evaluate an integrated disease management (IPM) strategy.

One of the main challenges remains the detection of Verticillium dahliae in the field, as already highlighted in the previous Pathoflax project. To better characterize the susceptibility of the varieties to diseases, the project is making use of LITERAL — a portable phenotyping device that uses high-resolution imagery to measure greenness, crop height, canopy cover, and emergence. The aim is to identify specific secondary symptoms that could be linked to the disease, enabling faster detection and earlier intervention.

Published on 7/8/26