Phaeophyscia orbicularis

Phaeophyscia orbicularis is a foliose lichen frequently observed on the bark of deciduous trees, stone surfaces, and concrete. While not a pathogenic fungus in the traditional sense, it acts as an epiphyte. In an agronomic context, it is often seen as a symptom of a tree’s declining health or slow bark expansion, as it primarily colonizes stable, mature surfaces.

The lichen primarily affects tree species with rough or aging bark. It is most commonly found in orchards that have not received regular maintenance, such as pruning or thinning, which creates microclimates favorable for colonization. It is rarely a problem for young, fast-growing trees because the expanding bark prevents the lichen from anchoring securely.

The visual symptoms include small, circular, flattened thalli that are typically dark grey to brownish-black in color. The lobes at the edges of the lichen are often lighter in color. As these patches mature, they coalesce to form larger, crust-like colonies that can eventually cover large areas of the trunk and branches, masking the underlying bark conditions.

Development and spread are facilitated by prolonged periods of high humidity and shade. Poor air circulation within a tree's canopy creates an ideal environment for the lichen to thrive. Although the lichen itself does not extract nutrients from the tree, its persistent presence can hold moisture against the bark, creating a breeding ground for wood-decaying organisms and pests.

Management strategies focus on improving tree vigor and sanitation. Regular pruning to increase sunlight penetration and air circulation is the most effective preventative measure. If the coverage is extensive, mechanical removal using a soft brush during damp weather is recommended, followed by the application of horticultural lime or copper-based washes to sanitize the bark and prevent recurrence.