Hysterium pulicare

Hysterium pulicare is a species of saprotrophic and occasionally facultative parasitic fungus from the order Hysteriales. It primarily inhabits the bark of various deciduous trees, where it develops its characteristic reproductive structures. While often considered a secondary invader, it plays a significant role in the degradation of bark tissue on weakened or stressed host plants.

The fungus is commonly found on various hardwoods, including oak, birch, hornbeam, and other broad-leaved species. It tends to colonize branches and trunks that have already suffered from environmental stress, such as frost cracks, sunscald, or mechanical wounds, effectively colonizing the cambium area and accelerating tissue necrosis.

The visual symptoms are quite distinctive: small, elongated, black, fissure-like fruiting bodies (hysterothecia) appear on the surface of the bark. These structures, often described as flea-like due to their shape and size, are densely packed in groups. As the infection progresses, the underlying bark becomes brittle, develops longitudinal cracks, and eventually detaches from the wood.

Environmental conditions conducive to the development of Hysterium pulicare include high humidity, stagnant air, and long periods of moisture. The fungus thrives in shaded, dense forest stands or poorly managed orchards. Spores are primarily disseminated by wind and rainwater, allowing the fungus to spread rapidly during wet seasons to new susceptible bark surfaces.

Management strategies focus on promoting tree vigor and maintaining sanitation. Essential practices include the regular removal of dead or dying branches, immediate treatment of bark wounds, and proper spacing of trees to ensure good air circulation. In cases of significant infestation, pruning and destruction of infected material are necessary to reduce the spore load and prevent further spread.