Melogramma gyrosum

Melogramma gyrosum is a species of ascomycete fungus known to colonize the bark of various hardwood trees. It typically acts as a necrotrophic pathogen, exploiting trees that are already stressed by environmental factors such as drought, frost, or physical damage. The fungus is characterized by its distinct stromata, which develop within the bark and eventually rupture the surface to release spores for reproduction.

The primary hosts for this fungus include species within the genus Quercus (oaks), as well as Fagus (beech) and Carpinus (hornbeam). It generally colonizes the woody parts of the tree, starting from small twigs and potentially progressing to larger branches. By disrupting the integrity of the bark, the fungus interferes with the tree's vascular transport, which can lead to localized cell death and overall vigor decline.

The visible signs of infestation involve the formation of gyrose or wavy-patterned stromata on the bark surface, which are dark in color. As the infection progresses, the bark in the affected area may become fissured, dry, and brittle. A significant symptom is the gradual dieback of small branches, which often gives the tree a sparse or stunted appearance in the affected crown sections.

Environmental conditions play a crucial role in the development and spread of Melogramma gyrosum. High humidity levels and poor air circulation within the canopy create ideal conditions for fungal growth and spore dispersal. The disease spreads primarily via wind-blown ascospores during rainy periods. Trees with high planting density are particularly susceptible because moisture persists longer on the bark, allowing for faster spore germination.

Managing the impact of this fungus requires a multifaceted approach focused on sanitation and tree vigor. Key strategies include the prompt removal of infected branches to reduce inoculum sources and avoiding the wounding of trunks during maintenance. Maintaining adequate space between trees to ensure good air circulation is essential for reducing humidity in the canopy. In cases of significant infection, systemic fungicides may be applied, though proper cultural practices remain the foundation of effective control.