Phlyctis

Phlyctis is a genus of crustose lichens that often grow on the bark of trees and shrubs. While gardeners sometimes mistake it for a parasitic plant disease, it is technically an epiphyte. This means the lichen uses the tree only as a physical substrate for anchoring, relying on photosynthesis and moisture from the air rather than draining nutrients or sap from the host plant.

The organism is a symbiotic association between a fungus and algae. While it does not kill the tree directly, Phlyctis can become problematic in orchard management. A heavy accumulation of lichens on the bark can trap moisture, providing a humid environment where harmful fungi, bacteria, and overwintering insect pests can flourish, hidden from the effects of sprays and predators.

Symptoms of its presence include flattened, pale-grey to white patches on the trunk or branches. The surface often appears powdery or granular. Unlike active bacterial or fungal diseases, these patches do not cause lesions, cankers, or soft rot. However, their physical presence can make it difficult for the observer to inspect the bark for early signs of actual tree diseases or pest infestations.

Conditions that favor the development of Phlyctis include high atmospheric humidity, poor air circulation, and slow growth of the host tree. It is most commonly found in older, neglected orchards or in areas with high rainfall. Trees with rough, textured bark offer more surface area for the spores to germinate, allowing the lichen to spread more effectively over time.

Effective management and prevention strategies include:

• Pruning branches to improve light penetration and air circulation.
• Physical removal of excessive lichen growth using non-damaging brushes.
• Applying a lime wash or copper-based sprays to the trunks to sanitize the bark.
• Maintaining tree health through proper fertilization and watering to promote vigorous bark growth.