Nephroma

Nephroma is a genus of foliose lichens that is often mistakenly classified as a plant disease by amateur gardeners. In reality, it is an epiphyte that lives on the surface of tree bark. It does not penetrate the host's tissues or act as a pathogen, meaning it does not cause biological infection or decay in the way fungi or bacteria do.

The organism consists of a symbiotic relationship between a fungus and either green algae or cyanobacteria. Because Nephroma is highly sensitive to air pollution, its presence on your trees is actually a sign of good air quality in your growing area. It derives its nutrients entirely from the atmosphere rather than from the host tree.

This lichen is commonly found on mature fruit trees and hardwood species, particularly in regions with high humidity. It colonizes trees with rough, stable bark where spores can easily latch on and grow. Since it thrives in moist, shaded environments, it is most prevalent in neglected or dense orchards where sunlight does not reach the stems.

While Nephroma is not inherently harmful, a heavy accumulation of lichen can harbor pests, mites, or spores of pathogenic fungi underneath its layers. Furthermore, if it covers a significant portion of the bark, it may slightly restrict the gas exchange required for the tree to breathe, potentially weakening the bark's overall resistance to environmental stress.

Effective management includes maintaining proper tree spacing and regular pruning to ensure good airflow and sunlight penetration, which naturally inhibits lichen growth. For physical removal, gardeners should gently scrape off the lichen during dormant seasons or apply a lime wash, which creates an alkaline surface that discourages the attachment of Nephroma.