Thelenellaceae lichens

The family Thelenellaceae represents a group of lichenized fungi commonly found on tree bark. In agricultural contexts, they are frequently misidentified as plant diseases; however, they are technically epiphytes. They do not feed on the host plant, and their presence does not classify them as pathogens in the traditional pathological sense.

The biological nature of these organisms involves a symbiotic relationship between an ascomycete fungus and algal or cyanobacterial partners. Unlike parasitic fungi that invade living tissues, draw nutrients, and cause cell death, Thelenellaceae simply use the tree bark as a physical anchor, exerting no physiological stress on the host plant.

These lichens thrive on various perennial crops, particularly in older orchards where trees have developed rough, mature bark. They are most common on apple, pear, and plum trees. Because they do not penetrate the cambium or wood, the trees remain healthy, and the presence of lichens is rarely a primary concern for fruit production.

Symptoms are identified by the appearance of crust-like or flaky patches on the trunks and main branches. These structures vary in color but are distinct from actual bark lesions or cankers. They can be easily scraped off without revealing any internal tissue damage, rotting, or underlying necrotic areas typical of invasive plant diseases.

• Environment: High humidity and low sunlight promote growth.
• Aesthetic Impact: May signify an older or unpruned orchard.
• Risk: Potential hiding spot for insect pests like scale or mites.

Management and prevention involve improving the overall health and airflow of the orchard. Pruning to open the canopy, removing dead wood, and maintaining tree vigor are the best practices. Periodic scrubbing of the bark and applying whitewash can effectively reduce the colonization of these epiphytic organisms, preventing them from creating habitats for harmful insects.