Anisomeridium biforme

Anisomeridium biforme is a species of crustose lichen belonging to the group of pyrenocarpous fungi. In arboriculture and orchard management, it is classified as an epiphytic organism. While it does not directly parasitize the plant tissue, it inhabits the bark surface, reflecting the environmental conditions of the surrounding ecosystem and the physiological state of the host tree.

The lichen primarily colonizes the bark of various deciduous trees, including apple, pear, oak, and ash species. It thrives on substrates that are stable and relatively long-lasting. By attaching to the bark, it utilizes the tree as a physical support system rather than a source of nutrients, though it can influence the local microclimate of the bark surface.

Symptoms appear as small, often circular or irregular crusts or spots on the bark. These spots typically range from greyish-brown to olive-black in color. A defining characteristic is the presence of numerous minute, elevated dots representing the perithecia (fruiting bodies), which give the bark a distinct grainy or sandpapery texture upon close inspection.

Development is heavily dependent on environmental conditions, particularly humidity, shade, and air circulation. It is most commonly found in neglected orchards or dense forest stands where high moisture levels and low light create an ideal habitat. Trees with slow growth or thick, aging bark are the most susceptible to colonization by this organism.

The host trees may suffer indirectly from the dense growth of Anisomeridium biforme. The lichen layer can trap moisture, potentially promoting secondary bark rot and creating a micro-habitat for overwintering pests such as scale insects or mites. Effective control measures include:

• Pruning to improve light penetration and air circulation.
• Mechanical removal of lichen crusts using specialized brushes.
• Application of whitewash or copper-based treatments to sanitize the bark and inhibit spore germination.