Myxarium nucleatum

Myxarium nucleatum is a species of jelly fungus belonging to the family Exidiaceae. While it is primarily recognized as a saprotrophic organism that decays dead organic matter, it is often documented in arboriculture as a colonizer of weakened or damaged tree species. Its biological role involves the breakdown of wood cellulose and lignin, which can negatively impact the health of susceptible trees if left unchecked.

This fungus typically affects broad-leaved trees, including species of Acer (maple), Quercus (oak), and Fraxinus (ash). While it often targets dead branches or fallen logs, it may opportunistically colonize living trees that have been compromised by environmental stress, frost cracks, or improper pruning. The fungus thrives where the bark is thin or damaged, allowing the mycelium to penetrate deeper into the tree's vascular system.

The primary symptom of infection is the appearance of gelatinous, translucent, or whitish fruiting bodies on the bark surface. These structures contain distinct, firm, white inclusions that resemble small kernels or nuclei, which give the fungus its scientific name. As the infection progresses, the affected areas may show signs of tissue necrosis, cracking, and structural decay, leading to localized dieback of the bark.

The development of Myxarium nucleatum is strongly favored by high humidity and moderate temperatures. The fungus releases spores that are easily disseminated by wind or rain splash. Once they land on a suitable moist surface, such as a fresh pruning wound, the spores germinate and begin to form a mycelial mat that colonizes the wood surface, especially during wet seasons or in shaded, poorly ventilated environments.

Effective management strategies center on maintaining overall tree vigor and minimizing exposure points for pathogens. Best practices include:

• Regular sanitation pruning to remove dead or infected wood.
• Sterilizing all pruning tools with a disinfectant solution between trees.
• Applying wound sealants to major cuts to prevent fungal entry.
• Improving site drainage and air circulation to reduce the humidity levels that favor fungal growth.