Bierzo chestnut fungus risk rises to record 58%

The Mesa del Castaño del Bierzo has reported a significant increase in the risk of the fungus Sirococcus smithogilvyi within the chestnut groves of the Bierzo region. Following a period of decline between 2023 and 2025, where average positivity rates dropped from 33% to 14%, the 2026 campaign shows a surge to an average of 58% across sampled locations. This represents the highest level recorded in the current monitoring series.

Statistical analysis suggests this increase is widespread and not tied to a specific chestnut variety, pointing instead to environmental or meteorological factors that may have favored the pathogen. While the risk level is high, officials advise prudence, noting that the presence of the fungus in the groves does not always translate to an equal intensity of impact on the fruit itself. Factors such as the specific fungal strain, biological limiting organisms, and post-harvest environmental conditions also play critical roles.

To mitigate risks, the Mesa del Castaño recommends following the EUROCASTANEA protocol. Suggested measures include prioritizing mechanical harvesting, accelerating collection to prevent chestnuts from sitting on the ground overnight, and ensuring trees are properly pruned and fertilized. Producers are advised to watch for brown discoloration on the burrs as a visual indicator of potential infection.