Iris leaf spot

Systematic position and nature of the pathogen. The causal agent Heterosporium tortuosoinflatum is classified within the kingdom Fungi and the genus Heterosporium. This phytopathogen is highly specialized and is widely recognized as the primary cause of leaf spot disease in various iris species, causing significant damage to horticultural plantings.

Diseases and host plants. The fungus causes a disease known as Iris leaf spot. The infection is characterized by the appearance of small, brown, water-soaked spots on the leaves, which eventually expand into elongated, oval lesions with a grayish center and a distinct dark margin. Severely infected leaves may wither and die prematurely.

Biology and life cycle. The pathogen overwinters primarily as mycelium and conidia in infected plant debris left in the soil. During periods of high humidity and moderate temperatures in the spring, the fungus produces new spores that are disseminated by wind and splashing rain. These spores infect healthy foliage, continuing the cycle throughout the growing season.

Conditions for development and harmfulness. Development is favored by high humidity, frequent rainfall, and poor air circulation within dense plantings. The pathogen thrives in temperatures between 15°C and 22°C. The economic impact includes a severe reduction in plant vigor, inhibition of flower bud formation, and the potential loss of entire collections due to chronic infection.

Protection and control measures. Management strategies should be integrated to reduce disease pressure:

• Strict sanitation, including the removal and destruction of all infected foliage in the autumn.
• Ensuring adequate spacing between plants to improve airflow and reduce leaf wetness.
• Application of appropriate fungicides containing copper or systemic triazole compounds during the active growing phase.
• Avoiding overhead irrigation to prevent the splashing of spores onto foliage.