Haematomma vulgare

Haematomma vulgare is a type of crustose lichen that often colonizes the bark of mature trees. While it is biologically classified as a composite organism formed by a symbiotic relationship between a fungus and algae, in agricultural practice, its dense colonization is often perceived as a sign of poor tree vitality or lack of proper horticultural maintenance.

This lichen is most commonly found on the trunks and skeletal branches of deciduous fruit trees, such as apple and pear. It prefers surfaces with high moisture levels and limited exposure to direct sunlight. The rough texture of older tree bark provides the perfect substrate for the spores to germinate and for the lichen to form its persistent, spreading crust-like colonies.

The primary symptoms of its presence include the formation of whitish-grey crusts on the bark surface, punctuated by distinctive reddish or orange apothecia (fruiting bodies). As the lichen spreads, it may cover large areas of the trunk, masking potential structural defects in the bark and preventing the tree from shedding dead tissue naturally, which is a vital part of its growth process.

The development of Haematomma vulgare is strongly correlated with high environmental humidity and poor air circulation within the orchard canopy. Trees that are not pruned properly or that grow in overly dense, shaded environments are particularly susceptible to widespread colonization. These conditions create a microclimate that allows the lichen to thrive throughout the year.

The impact of this lichen on agricultural crops is primarily indirect but significant. It creates a refuge for pests such as scale insects and spider mites and provides a damp environment conducive to the colonization of harmful fungal pathogens. Effective control measures include:

• Mechanical removal of old bark using specialized brushes or scrapers during dormancy.
• Application of dormant sprays, such as iron or copper sulfate, to disinfect the bark surface.
• Implementation of regular pruning practices to ensure sunlight penetration and improved airflow within the crown.

By maintaining proper hygiene in the orchard, growers can prevent the excessive accumulation of lichens, thereby promoting better tree vigor and reducing the habitats available to harmful organisms.