Roccella

Roccella is a genus of lichen frequently encountered on tree trunks, often misidentified by growers as a parasitic disease. While not a pathogenic agent in itself, its presence is a clear agronomic indicator of environmental conditions and tree vitality.

Biologically, Roccella is an epiphyte—a symbiotic organism consisting of fungi and algae that uses the tree bark solely as a physical anchor. Unlike parasitic fungi, it does not extract nutrients from the host plant's tissues, meaning it is technically not an infectious disease.

It typically colonizes older fruit trees such as apples, pears, and plums, as well as various ornamental species. Its growth is primarily favored by high humidity, low light levels, and poor airflow within the canopy, which often coincides with neglected or elderly trees.

The primary symptom is the appearance of shrubby, leathery thalli covering the bark. While the lichen itself is harmless, its physical density provides a shelter for overwintering pests like scale insects and mites, and can trap moisture that promotes the growth of secondary bacterial or fungal infections.

Effective prevention and control focus on improving tree vigor and air circulation. Recommended practices include:

• regular crown pruning to allow sunlight penetration;
• mechanical removal of old, flaky bark;
• applying whitewash (lime treatment) to trunks;
• optimizing irrigation to prevent excessive humidity in the orchard environment.