Lepraria

Lepraria is a genus of crustose lichens that often colonize the bark of trees and shrubs. While they are not parasitic in the sense of feeding on the plant's nutrients, they act as epiphytes that can significantly impact the health of mature or stressed trees if left unchecked for long periods.

The organism consists of a fungal partner and an algal partner living in symbiosis. It does not penetrate the host's living tissues but forms a thick, dusty covering on the surface of the bark. This layer can trap moisture and harbor secondary pests, while simultaneously restricting the tree's ability to undergo essential gas exchange.

Various tree species, particularly apple, pear, and certain ornamental hardwoods, are susceptible to Lepraria. The development of the lichen is heavily influenced by environmental factors such as high humidity, low sunlight, and stagnant air conditions, which are commonly found in unpruned or neglected gardens.

The primary symptom is a distinct, powdery, or granular crust-like coating on the trunk and branches. It usually appears as a pale green, grey, or white color. Unlike other types of lichen, Lepraria lacks a structured thallus and appears more like a diffuse layer of loose particles that can easily rub off.

Effective management focuses on improving tree vigor and environmental conditions. Strategies include:

• Scraping away the lichen from the bark using specialized brushes.
• Applying whitewash treatments to the trunk to sanitize the bark surface.
• Thinning the canopy to increase light penetration and airflow through the tree.
• Ensuring proper soil nutrition to help the tree outgrow the lichen infestation.