Diapleella coniothyrium

Diapleella coniothyrium (formerly known as Leptosphaeria coniothyrium) is a fungal plant pathogen responsible for cane blight, a severe disease affecting raspberries, blackberries, and other Rubus species. This ascomycete fungus causes localized necrosis of the stems, leading to vascular disruption and the subsequent wilting or death of the affected canes.

Symptoms typically manifest as purplish or dark brown lesions surrounding the nodes where leaves attach to the stem. Over time, these lesions enlarge and crack the bark, exposing the underlying wood. As the disease progresses, the stem becomes brittle and may collapse, preventing the transport of water and nutrients to the fruiting lateral branches.

The life cycle of the pathogen involves both sexual (ascospores) and asexual (conidia) reproductive structures. The fungus overwinters primarily in infected cane stubs and plant debris on the soil surface. During wet weather, spores are dispersed by splashing raindrops or wind onto new vegetative growth, where they penetrate the host through wounds or natural openings.

Conditions favoring the spread of Diapleella coniothyrium include high humidity, frequent rainfall, and poor canopy airflow. The pathogen thrives in dense plantings where moisture remains trapped on the stems for long periods. Additionally, wounds caused by mechanical tools, frost, or insects such as the raspberry cane borer serve as entry points for the fungus.

Control strategies focus on sanitation and preventative measures:

• Prompt removal and destruction of infected canes immediately after harvest.
• Maintaining proper row spacing and pruning to promote good air circulation.
• Careful handling during cultivation to minimize mechanical damage to the canes.
• Application of protective fungicides during the early spring and before periods of anticipated heavy rainfall.