Letrouitiaceae

The Letrouitiaceae family consists of a group of lichenized fungi belonging to the order Lecanorales. In agricultural and forestry terms, these organisms are generally considered epiphytes rather than active plant pathogens, as they primarily colonize the bark of trees without penetrating deeper wood tissues to derive nutrients.

The causal agents are fungi within the genus Letrouitia. These organisms establish a symbiotic relationship with algal partners to form a lichen thallus. While they do not directly cause internal rot or systemic disease, their proliferation on the surface of branches and trunks can interfere with the physiological function of lenticels and bark gas exchange.

These fungi are found on a variety of broad-leaved trees and occasionally on fruit trees in orchards with high humidity. They are most common on older trees where the bark provides a stable, long-term substrate for colonization, particularly in environments with limited air movement and high moisture retention.

Symptoms of the presence of Letrouitiaceae include distinct, brightly colored crustose or squamulose thalli. These are often observed as patches of orange, yellow, or reddish-brown pigment on the bark surface. Unlike necrotrophic pathogens, they do not cause visible tissue decay or bleeding cankers on the host plant.

Favorable conditions for their development are characterized by high humidity and moderate light levels. Prevention involves cultural practices such as canopy thinning to improve ventilation and sunlight penetration, which naturally limits the growth of epiphytes. If necessary, chemical control involves the application of copper-based fungicides, which effectively eradicate or suppress the growth of lichenized fungi on the bark surface.