Raspberry cane blight

Systematic position and nature of the pathogen: Leptosphaeria coniothyrium is an ascomycete fungus and the primary agent responsible for cane blight in bramble fruits. This pathogen specifically targets the vascular and cortical tissues of stems, leading to severe localized necrosis. It is a persistent soil-borne and air-borne fungus that poses a significant challenge to both commercial raspberry growers and home gardeners.

Affected crops and symptoms: The fungus primarily affects Rubus species, including red and black raspberries, as well as blackberries. Symptoms typically appear in summer as dark, purplish-brown lesions around buds. As the infection progresses, the lesions expand and girdle the stem, causing the canes to wilt, crack, and eventually die. The wood beneath the lesions often becomes brittle and discolored.

Biology and life cycle: The pathogen overwinters as mycelium and pycnidia in infected canes and leaf debris. During wet spring weather, the fungus releases conidia that are splashed by rain or wind-dispersed to healthy tissues. The infection requires an entry point, such as wounds caused by the raspberry cane midge, pruning shears, or physical damage from environmental factors.

Environmental conditions and impact: Disease development is favored by prolonged periods of high humidity, frequent rainfall, and warm temperatures. Dense, unpruned plantations provide an ideal microclimate for the fungus to thrive. The overall damage is manifested in reduced fruit yield, lower fruit quality, and in severe cases, the total death of the canes during the subsequent winter due to weakened resistance to frost.

Control and management measures: Effective management of cane blight requires a multi-faceted approach to reduce the inoculum pressure:

• Sanitation: Pruning and burning infected canes immediately after harvest is critical.
• Pest management: Controlling insects like the cane midge to prevent entry wounds.
• Spacing: Ensuring adequate spacing and training of canes to improve air circulation and sunlight penetration.
• Fungicide application: Utilizing protective fungicides during the pre-blossom and post-harvest stages when environmental conditions are conducive to infection.