Calendula leaf smut

Calendula leaf smut, caused by the fungus Entyloma calendulae, is a specific fungal disease that affects marigold plants. It is a significant concern for gardeners and farmers aiming to produce high-quality medicinal or ornamental calendula flowers.

The disease primarily targets Calendula officinalis. While it rarely kills the plant outright, it causes severe defoliation, which negatively impacts the overall health and productivity of the crop.

Symptoms appear as small, pale-green or yellowish spots on the leaves. As the infection progresses, these spots expand, turn brown, and become necrotic. In high-humidity conditions, one can observe a faint greyish fungal mass on the underside of the leaves, corresponding to the sporulation of the pathogen.

The development of Entyloma calendulae is favored by cool, moist conditions with temperatures ranging between 15°C and 22°C. Rain splashes and wind currents are the primary vectors for spore dispersal. The fungus overwintering in debris ensures a recurring cycle of infection in the following growing season.

Effective management requires an integrated approach to reduce disease pressure. Key strategies include:

• Prompt removal and destruction of infected plant debris to minimize inoculum.
• Ensuring proper plant spacing to improve airflow and reduce humidity around the foliage.
• Applying fungicides specifically labeled for fungal leaf spots when initial symptoms are observed.
• Implementing crop rotation to prevent the buildup of soil-borne spores.