Pertusariaceae

Pertusariaceae is a family of ascomycetous fungi that exists primarily in the form of lichens. While often mistaken for a plant disease, they act as epiphytes rather than active pathogens. They attach themselves to the bark of trees and shrubs, using the surface as a physical substrate for growth without directly penetrating or consuming the living tissues of the host plant.

These lichens commonly affect a variety of woody plants, particularly older fruit trees like apples, pears, and stone fruits. They thrive on the rugged, aging bark of mature trees, where the surface texture is stable and provides adequate space for the lichen thallus to anchor and expand over time, taking advantage of the accumulation of microscopic organic debris.

Symptoms are identified by the presence of crustose or bushy growths on trunks and branches. These growths can be grayish, yellowish, or green, often giving the bark a weathered or textured appearance. While they are not inherently toxic to the tree, excessive coverage can trap excess moisture against the bark and provide protected habitats for overwintering insect pests like scale insects or mites.

The development of Pertusariaceae is strictly dictated by environmental factors, most importantly high relative humidity and low light levels. They are most prevalent in orchards with poor pruning practices, dense canopy coverage, and lack of regular maintenance. Stagnant air and consistently damp bark surfaces are the primary drivers for their rapid colonization and spread.

To prevent or manage these epiphytes, orchardists should focus on improving tree vigor and bark hygiene. Regular sanitation, which includes thinning the canopy to allow for better light penetration and airflow, is essential. Additionally, physically scraping away dead bark and applying horticultural whitewash or copper-based sprays during the dormant season helps maintain a clean, inhospitable environment for lichen attachment.