Collema

Collema is a genus of gelatinous lichens that often colonize the bark of trees and shrubs. While they are not pathogens that derive nutrients directly from the plant, their presence is frequently associated with poor tree vigor and can be considered an indicator of environmental conditions that favor other diseases.

This organism commonly affects fruit trees, particularly those in older, unmanaged, or high-humidity orchards. It acts as an epiphyte, colonizing the bark surface and taking advantage of the crevices and moisture trapped within the protective layers of the tree.

The visual symptoms of Collema include the appearance of dark, leaf-like or lobed structures that swell and become gelatinous when wet. During dry weather, these structures shrink and appear as dark, brittle, and often overlooked crusts on the wood surface.

The spread of Collema is facilitated by high humidity, poor sunlight penetration, and inadequate orchard hygiene. Trees with stagnant airflow in their canopy are particularly susceptible, as constant moisture prevents the bark from drying out sufficiently to inhibit lichen colonization.

While not directly lethal, its presence is detrimental as it creates a habitat for harmful insects and fungal spores. Effective prevention and control include:

• regular pruning to improve air circulation;
• manual cleaning of the bark during the dormant season;
• applying lime wash to tree trunks;
• using copper-based fungicides when necessary to manage bark microflora.