Verrucaria

Verrucaria is a genus of fungi belonging to the class Lecanoromycetes. In an agronomic context, while many species are considered lichenized, their presence on the bark of fruit trees and ornamental shrubs is often classified as a detrimental condition that impedes the health and vigor of the host plant by covering the surface and trapping moisture.

The causal agent is the fungal organism that forms tiny, wart-like fruiting bodies (perithecia) on the bark surface. This is primarily an epiphytic interaction that can shift to a parasitic behavior, where the fungus competes for space and creates a barrier that inhibits normal respiration and metabolic processes of the tree's outer layer.

This condition affects a variety of woody plants, especially those in poorly ventilated or excessively humid microclimates. Common hosts include pome fruit trees like apples and pears, as well as deciduous ornamental species. Mature trees with rough, aged bark are significantly more susceptible to colonization compared to younger, smoother-barked individuals.

Key symptoms include the development of dark, bumpy, or crust-like spots on the trunk and primary branches. These spots appear as distinct, hardened growths. If left untreated, the affected areas may lead to localized bark necrosis, cracking, and a general decline in the plant's overall vitality, making it more susceptible to secondary pests and pathogens.

Environmental conditions favoring the development of Verrucaria include high humidity, stagnant air, and low sunlight exposure. Management and prevention strategies focus on improving tree health and air circulation. Regular pruning to thin out the canopy is essential, along with mechanical cleaning of the bark using stiff brushes. During the dormant season, application of copper-based fungicides can help manage the fungal population and prevent further spread.