Verrucariaceae lichens

The Verrucariaceae family consists of a group of lichenized fungi. In terms of agronomy, they are not classified as a disease but as epiphytes. These organisms use the bark of trees primarily as a substrate for anchoring. Unlike pathogenic fungi, they do not penetrate the internal tissues of the tree or derive nutrients from the host's sap.

These lichens typically colonize a variety of fruit trees, including apples, pears, and stone fruits. They demonstrate a preference for older, mature trees that have developed rough, fissured bark. This texture provides numerous crevices where moisture and dust can accumulate, facilitating the attachment and growth of these organisms in a stable environment.

The visual symptoms of a Verrucariaceae presence include the formation of crustose, plaque-like spots on the trunk and primary branches. These patches are often firmly attached to the bark, making them difficult to remove without mechanical intervention. While they do not directly cause necrosis, their excessive presence often indicates that the tree's bark is ageing and the tree itself may be lacking vigour.

The development of these organisms is heavily influenced by environmental factors such as high humidity, poor air circulation within the tree canopy, and low light intensity. Orchards that are neglected or planted in areas with poor ventilation provide an ideal microclimate. As the lichen grows, it modifies the surface of the bark, potentially keeping it wetter for longer periods.

The primary economic impact of Verrucariaceae is indirect. While they are not harmful to the plant's metabolism, their dense layers on the bark can provide a protective habitat for overwintering pests, such as scale insects and spider mites, as well as harbor spores of pathogenic fungi. Effective management strategies include:

• Pruning to ensure better light penetration and air movement.
• Mechanical cleaning of the bark using specialized brushes.
• Applying whitewash or lime solutions to the trunks.
• Using copper or iron sulfate sprays to inhibit lichen growth and sanitize the surface.