Raspberry cane spot

Systematic position and type of pathogen: Gnomonia rubi is an ascomycete fungus belonging to the Gnomoniaceae family within the order Diaporthales. It functions as a specialized plant pathogen, commonly known for inducing stem lesions in various species of the Rubus genus, particularly in cultivated raspberries and blackberries.

Diseases and host plants: The fungus is responsible for the disease known as cane spot or spur blight on raspberries. It primarily targets the canes, petioles, and fruiting laterals. The initial symptoms appear as small, brownish spots that gradually expand, often coalescing into larger lesions that girdle the stem, leading to cane cracking and tissue necrosis.

Biology and life cycle: The pathogen overwinters as perithecia within the tissue of infected canes left on the ground or remaining on the plant. In spring, moisture triggers the release of ascospores, which are disseminated by wind and splashing rain. Upon reaching susceptible host tissue, the spores germinate and initiate the infection, which then produces conidia (pycnidia) to facilitate secondary infections throughout the growing season.

Conditions for development and severity: High humidity, frequent rainfall, and poor air circulation within the canopy are critical factors for the spread of Gnomonia rubi. The disease is particularly severe in dense plantations. Its economic impact is significant, as it reduces plant vigor, causes premature leaf drop, weakens the canes against winter frost, and leads to substantial yield losses.

Protection and control measures: Management of the disease requires an integrated approach:

• Sanitation: Pruning and removing infected canes immediately after harvest is crucial to reduce inoculum.
• Canopy management: Thinning out canes to ensure adequate sunlight and air movement.
• Chemical control: Applying copper-based sprays or systemic fungicides during early leaf development and before the onset of heavy rains.
• Variety selection: Utilizing raspberry cultivars that demonstrate higher resistance to fungal stem diseases.