Ramularia leaf spot of moonwort

Pathogen and disease type. Ramularia botrychii is a pathogenic fungus responsible for causing leaf spot disease in specific fern species. Classified as an anamorph fungus, it infiltrates the leaf tissue, leading to localized necrosis. The pathogen reproduces via conidia, which are small spores that serve as the primary source of infection spread.

Host plants. This fungus is host-specific, primarily targeting plants within the genus Botrychium (moonwort). Because these plants are often sensitive to environmental changes and are prized in botanical research and conservation, the impact of Ramularia botrychii can be significant for maintaining healthy populations of these ferns.

Symptoms and signs. The infection starts as small, chlorotic spots on the fronds of the moonwort. As the fungus colonizes the leaf cells, these spots expand and turn brown or grayish. In humid environments, a white, powdery fungal growth often appears on the underside of the affected leaf, marking the sites where conidiophores emerge to release spores.

Environmental conditions. The development of the disease is highly dependent on humidity and temperature. Ramularia botrychii thrives in cool, damp conditions where foliage remains wet for extended periods. Rain splashes and wind are the main vectors that transport spores from infected tissues to healthy leaves, allowing the disease to progress quickly in dense groups of plants.

Harmfulness and protection measures. The fungus causes premature leaf senescence and reduces the plant's ability to undergo photosynthesis, eventually weakening the entire specimen. Protection strategies focus on cultural practices:

• Remove and destroy infected fronds to prevent inoculum buildup.
• Improve air circulation around plants to reduce humidity levels.
• Avoid overhead watering to keep foliage dry.
• Apply targeted fungicides if the infection becomes widespread in a controlled environment.