Verrucariales fungi

The order Verrucariales consists mainly of lichenized fungi that live on the surface of various substrates, including the bark of woody plants. While they are not primary pathogens in the traditional sense, their growth on fruit trees is often considered an indicator of poor bark health and a precursor to more severe phytosanitary issues within the orchard.

These fungi belong to the class Eurotiomycetes. Their interaction with the host plant is primarily epiphytic. Although they do not directly invade the host's living tissues, they form dense colonies that can mask deeper problems, such as necrotic lesions or bacterial colonization, which are hidden beneath the layers of these fungal growths.

They commonly affect older perennial crops, such as apple, pear, and cherry trees. The fungi colonize areas of the bark that remain shaded and humid for extended periods. In poorly managed orchards, their presence can become widespread, covering the trunk and scaffold branches and effectively sealing off the bark surface.

The development of Verrucariales is driven by high humidity and limited sunlight exposure. Poorly ventilated orchards with low air circulation and high precipitation levels provide ideal conditions for their establishment. These fungi thrive in the moist microclimate created by dense canopy structures.

The damage caused by these organisms is indirect but significant. By covering the bark, they impede gas exchange, trap moisture against the tree surface, and provide a habitat for various pests and secondary pathogens. This condition stresses the tree and can lead to bark decay or increased susceptibility to frost damage.

Effective prevention and control methods include:

• Regular mechanical cleaning of tree trunks to remove old, dead bark and fungal colonies.
• Whitewashing trunks to protect bark and prevent colonization.
• Pruning to ensure optimal light and airflow within the canopy.
• Routine fungicidal applications during the dormant season to maintain clean bark surfaces.