Arthoniaceae lichens

The Arthoniaceae family represents a diverse group of lichens frequently observed on the trunks and branches of woody plants. While they are often mistakenly identified as pathogenic fungi, they are actually symbiotic organisms. In an agronomic context, their presence is rarely the primary cause of plant death, but rather an indicator of a tree's slow growth or an aged, compromised bark structure.

These lichens target a wide range of fruit trees, including pome and stone fruits. Being epiphytic, they do not extract nutrients from the host plant's internal tissues. However, the density of their growth can obstruct lenticels, which are essential for gas exchange, thereby negatively impacting the respiration of the bark tissues and potentially weakening the tree's overall vitality over time.

The symptoms of Arthoniaceae colonization include the appearance of crust-like or spotty growth on the bark. These patches may vary in hue, ranging from dull gray to dark brown, and they typically remain on the surface without causing deep lesions or rotting. Unlike parasitic fungi, they do not penetrate the cambium, which is the key distinction for agronomists evaluating orchard health.

Conditions that favor the spread of these organisms include high humidity, poor sunlight penetration, and dense, unpruned canopies. In commercial and home orchards, poor airflow combined with stagnant moisture creates the perfect microclimate for lichen spores to settle and develop. They are most commonly found in older, neglected orchards that lack proper maintenance programs.

Management of Arthoniaceae should focus on horticultural practices that promote tree vigor. Effective control measures include:

• Regular pruning to improve air circulation and sunlight exposure.
• Mechanical removal of loose, dead bark, which serves as a substrate for lichens.
• Periodic application of dormant sprays, such as iron sulfate, to clean the trunk.
• Ensuring proper soil nutrition to maintain the tree's health and vigorous growth cycles.