Brunneosphaerella leaf spot

Pathogen and disease type. Brunneosphaerella leaf spot is a fungal disease caused by the ascomycete Brunneosphaerella roupeliae. This pathogen is known for its ability to colonize host plant tissues, primarily leaves, leading to the formation of localized necrotic lesions. The disease is characterized as a fungal leaf spot, which can impede the plant's metabolic processes.

Affected crops. The disease primarily affects members of the Apocynaceae family, with Strophanthus gratus being the most commonly cited host. The fungus targets the leaves, where it interferes with the plant's ability to produce energy through photosynthesis. While primarily foliar, it can impact the overall vigor and growth rate of the ornamental or medicinal plants it infects.

Symptoms and signs. The infection begins as small, discolored spots on the leaf surface. As the fungus matures, these spots expand, turning brown or dark grey, often with a distinct border. Under conditions of high relative humidity, you may observe the production of fungal reproductive structures (fruiting bodies) within these spots. Severe cases result in leaf necrosis, chlorosis, and premature senescence or abscission of the leaves.

Environmental conditions and impact. The development of Brunneosphaerella roupeliae is favored by warm, humid environments. In nursery settings or greenhouse conditions, poor aeration and canopy density are critical factors that facilitate the rapid spread of conidia. The disease impact is significant as it reduces the green surface area of the plant, leading to stunted growth and potentially increased susceptibility to other environmental stressors.

Protection and prevention strategies. Management of this disease requires an integrated approach. Essential practices include:

• Removal and destruction of fallen leaves to reduce primary inoculum.
• Improving air circulation through proper plant spacing and pruning.
• Applying fungicides labeled for leaf spot diseases as a preventative or curative measure.