Raspberry leaf spot

Taxonomy and nature of the pathogen. Septoria rubi is a pathogenic fungus classified within the Ascomycota division. It is the causal agent of Septoria leaf spot, a common and potentially damaging disease that affects various species within the Rubus genus, particularly raspberries and blackberries.

Disease and host plants. The pathogen specifically attacks raspberry and blackberry plants. The disease manifests as circular or angular spots on the leaves, which start as brown lesions and eventually turn whitish in the center with a dark, necrotic border. Later, numerous tiny black structures called pycnidia develop within these spots, containing the fungus spores.

Biology and life cycle. The fungus overwinters primarily as mycelium and pycnidia in diseased plant debris, fallen leaves, and on the canes. During the spring, when temperatures rise and moisture is available, the pycnidia release conidia. These spores are disseminated by rain splash and wind to new growth, initiating primary infections. Multiple cycles of spore production occur throughout the growing season, facilitating the rapid spread of the pathogen.

Conditions for development and harmfulness. Septoria rubi thrives in environments with high humidity and moderate temperatures. The damage caused by this fungus is significant: it leads to premature defoliation, which reduces the plant's photosynthetic capacity. Consequently, this weakens the bushes, diminishes fruit yield, and compromises the winter hardiness of the canes, often leading to dieback during cold weather.

Control and management measures. Integrated pest management (IPM) is essential for controlling leaf spot. Key strategies include:

• Pruning and destroying infected canes after harvest.
• Sanitizing the orchard by raking and removing fallen leaves in autumn.
• Maintaining proper plant spacing to improve airflow and reduce leaf wetness.
• Applying protective or systemic fungicides during the growing season when environmental conditions favor disease outbreaks.