Melanohalea exasperatula

Melanohalea exasperatula is a species of foliose lichen often found growing on the bark of fruit trees. While it is technically an epiphyte and does not directly feed on the plant, its presence is frequently associated with trees that are suffering from poor health, lack of light, or inadequate ventilation in the canopy.

This lichen is commonly observed on pome and stone fruit trees, including apple, pear, and cherry trees. It tends to colonize older, rougher bark surfaces, especially in orchards where maintenance has been neglected for several years, leading to dense canopies that trap moisture.

The primary symptoms of colonization include small, tightly appressed thalli that are typically brown or olive-brown in color. A distinctive feature of this species is the presence of small, granular outgrowths called isidia on the surface of the thallus, which help in distinguishing it from other similar lichen species.

Environmental conditions favoring the growth of Melanohalea exasperatula include high humidity levels, poor air circulation, and slow growth rates of the host tree. Because the bark is not shedding properly, the lichen has a stable substrate to establish and expand over time, often covering large areas of the trunk.

The harm caused by this organism is largely indirect. By covering the bark, it traps moisture and debris, creating a refuge for various tree pests and diseases. Management strategies focus on improving tree vigor, pruning for better sunlight penetration, and manual bark cleaning followed by the application of copper-based fungicides.

• Manual removal of lichen using soft brushes or scrapers.
• Application of lime wash on trunks.
• Pruning to increase airflow and light penetration.
• Application of authorized copper-based fungicides.