Trapeliaceae

Trapeliaceae is a family of crustose lichens that grow on various substrates, including the bark of trees. In agronomy, it is crucial to distinguish between true plant pathogens and epiphytic organisms. These lichens are not considered plant diseases because they do not extract nutrients from the host plant nor do they cause tissue necrosis or wilting. They are purely sessile, using the bark as a physical support system.

The biology of these organisms is based on a symbiotic relationship between a fungal partner and an algal photobiont. Unlike pathogenic fungi, they do not produce haustoria or invade the vascular tissue of the host. Their nutrition is derived from atmospheric deposition, dust, and rain. Therefore, their presence on trees is an ecological indicator of the environment rather than a symptom of a localized plant infection.

The appearance of these lichens involves crust-like, granular, or squamulose thalli. They typically have a greyish or greenish hue and produce reproductive structures known as apothecia. While they do not directly harm the tree, their dense accumulation may indicate that the tree's bark is aging or that the overall vitality of the tree has declined due to environmental stress or poor growth conditions.

Development and spread are primarily favored by high ambient humidity, low light levels within the canopy, and stagnant air. These conditions often occur in neglected orchards where pruning is insufficient. Because the lichens prefer stable, long-lasting surfaces, they thrive on older, slower-growing bark, which is why they are rarely a problem in young, rapidly growing orchards.

Management strategies for orchards with high lichen colonization focus on improving tree vigor and air circulation:

• Implementing regular pruning to increase light penetration and airflow.
• Manual mechanical cleaning of trunks and branches to remove accumulated crusts.
• Applying preventive sprays, such as copper-based formulations, which naturally inhibit lichen growth.
• Maintaining proper fertilization and irrigation schedules to promote vigorous bark expansion and regeneration.