Haematomma

Haematomma is a genus of crustose lichens that often colonize the bark of trees and shrubs. In an agronomic context, while they are not primary pathogens (fungi that cause rot or necrosis), they are categorized as undesirable epiphytes because their presence indicates poor tree vigor and creates an environment detrimental to overall plant health.

From a biological standpoint, Haematomma consists of a fungal partner and an algal component living in symbiosis. These lichens attach themselves to the bark surface, slowly expanding over time. They thrive in environments with high humidity and stagnant air, which is common in neglected orchards or areas with dense canopy cover.

The host range for Haematomma primarily includes various orchard trees, such as apple, pear, plum, and cherry trees. Older trees with rough, cracked bark are particularly susceptible to colonization. In woodlands, it can also be found on various hardwood species, taking advantage of stable microclimates on the tree trunk.

The primary concern regarding this lichen is that it serves as a harbor for pests and disease spores. Its complex structure protects overwintering insects like scale insects and mites from environmental stress and systemic pesticides. Furthermore, by covering the lenticels, the lichen can physically impede bark respiration, leading to localized physiological stress.

To control Haematomma, manual removal is the most effective approach. Using a blunt wooden or plastic scraper, one should carefully remove the lichen growths during the dormant season. After mechanical cleaning, applying a horticultural whitewash or a copper-based solution helps disinfect the bark. Regular pruning to improve canopy airflow is the best preventive strategy against recurrent lichen growth.