Rachicladosporium leaf spot of iris

The disease is caused by the fungal pathogen Rachicladosporium iridis. This fungus specifically targets plants of the Iris genus, causing necrotic spotting on foliage. It is considered a significant pathogen that affects both the health and the aesthetic appearance of various iris cultivars grown in gardens and commercial nurseries.

The host range is primarily focused on the genus Iris, including bearded, beardless, and bulbous iris types. Under favorable conditions, the disease spreads rapidly within a plant collection, especially in areas where plants are crowded and suffer from high humidity or poor air circulation.

The most common symptoms include elongated or irregular brown to dark spots on the leaves. As the infection progresses, the lesions expand, leading to chlorosis and tissue necrosis. In humid conditions, a sparse layer of fungal spores can often be observed within the necrotic areas, which serves as the primary inoculum for further spread.

Disease development is heavily influenced by environmental factors. High moisture levels, such as frequent rainfall, heavy dew, or overhead irrigation, create perfect conditions for spore germination and infection. The fungus persists in dead plant material left in the garden, providing a source of primary infection at the start of the next growing season.

Integrated pest management strategies are recommended for control. This includes maintaining proper plant spacing to improve airflow, removing and destroying all infected foliage at the end of the season to reduce inoculum, and avoiding overhead watering. When symptoms appear, the application of systemic or contact fungicides approved for ornamental plants can effectively manage the disease.