Lecidella

Lecidella is a genus of crustose lichens that often colonizes the bark of fruit trees. While lichens are not considered primary pathogens because they do not extract nutrients from the tree, their presence can indicate a micro-climatic imbalance in the orchard, specifically high humidity and lack of ventilation.

These lichens commonly affect mature apple, pear, and stone fruit trees. They thrive on the rough, fissured bark of older specimens, using it as a physical substrate for growth. Once established, they can spread rapidly across the trunk and structural branches, especially in neglected or poorly maintained orchards.

The visual symptoms of Lecidella include crusty, often grayish or yellowish patches appearing on the bark. Over time, these patches form small, distinct reproductive structures known as apothecia. If left untreated, the lichen layer can thicken, potentially inhibiting the bark's ability to breathe properly.

Growth and spread are heavily dependent on environmental factors, particularly prolonged moisture and shade. In overcrowded orchards with poor canopy airflow, the environment remains constantly damp, allowing lichen spores to germinate and colonize new bark surfaces more efficiently than in healthy, well-pruned trees.

The main hazard of Lecidella is that it creates a micro-habitat for overwintering pests, such as scales, mites, and various fungal spores. To maintain tree vitality, it is advised to use mechanical cleaning methods with firm brushes, followed by proper pruning to improve airflow. Maintaining overall tree vigor through adequate fertilization is the best preventive measure.