Stagonosporopsis leaf spot

Stagonosporopsis leaf spot is a fungal disease caused by the pathogen Stagonosporopsis rudbeckiae. This fungus specifically targets Rudbeckia species, leading to significant foliage damage that can ruin the visual appeal and overall health of these popular ornamental plants.

The host range is primarily limited to various cultivars of Rudbeckia. The pathogen attacks leaves, stems, and occasionally flower stalks, causing lesions that disrupt the photosynthetic capacity of the plant. If left untreated, the disease can cause severe defoliation during the growing season.

Symptomatology involves the appearance of irregular, brown, or grayish spots on the leaves. As the disease progresses, these spots often develop a yellow halo. Under magnification or close inspection, tiny black pycnidia may be visible within the necrotic tissue, which are the structures that hold the spores for further dissemination.

The development and spread of Stagonosporopsis rudbeckiae are highly dependent on environmental factors, particularly moisture and temperature. Extended periods of leaf wetness, high humidity, and poor airflow in dense plantings facilitate the germination and infection processes, allowing the fungus to spread rapidly across a garden bed.

• Remove and destroy infected plant debris.
• Avoid overhead irrigation to minimize leaf wetness.
• Ensure proper plant spacing to promote air circulation.
• Apply preventative fungicides during periods of high humidity.
• Practice crop rotation if soil-borne inoculum is suspected.