Cercospora leaf spot of Eustoma

The fungus Pseudocercospora eustomatis is the primary pathogen responsible for Cercospora leaf spot in Eustoma. This fungal disease is known for causing significant damage to the foliage, which leads to reduced ornamental value and overall plant vigor in commercial and garden settings.

The host range is primarily limited to Eustoma grandiflorum (commonly known as Lisianthus). The pathogen targets the leaves, and in severe cases, it may affect the stems and floral buds, leading to premature leaf drop and potential plant death if left untreated during critical growth stages.

Symptoms begin as small, irregular lesions that appear on the leaves. As the infection progresses, these spots turn light brown with darker, necrotic margins. Eventually, a grayish, fuzzy layer of conidia becomes visible on the underside of the leaf, which is a definitive sign of sporulation for this fungal species.

Environmental conditions play a crucial role in the development and spread of Pseudocercospora eustomatis. High humidity (above 80%), poor air circulation, and moisture persisting on the leaf surface for extended periods provide the perfect conditions for spore germination and rapid colonization of the host plant.

• Reduce leaf wetness by optimizing irrigation practices (drip irrigation is preferred).
• Ensure adequate spacing between plants to improve airflow in greenhouse environments.
• Implement strict sanitation measures by removing and disposing of infected plant debris.
• Apply preventative fungicides containing chlorothalonil, mancozeb, or strobilurins to control existing infections.