Raspberry cane blight

The fungus overwinters in the form of mycelium, pycnidia, and perithecia on infected canes and plant debris. In the spring, when temperatures rise and humidity remains high, the pathogen produces spores for infection.

The development of the disease is favored by temperatures between 15°C and 20°C and wet weather conditions. Spores are easily disseminated by splashing rain, wind, and insects throughout the field.

The fungus enters the host through natural wounds, cracks in the bark, or feeding punctures created by pests. It quickly colonizes the vascular tissues of the canes, disrupting the plant's ability to transport water and nutrients.

Leptosphaeria coniothyrium is highly persistent and can survive in the soil and on infected canes for several seasons, making long-term plantation management a challenge.

The infection causes large purple or brown lesions on the canes, which eventually lead to tissue necrosis and bark splitting. The cane structural integrity is compromised, making it prone to breakage.

Infected plants exhibit reduced winter hardiness, leading to significant frost damage during winter months. Fruit buds on infected canes often fail to develop or die prematurely in the spring.

Yield loss is the most severe economic impact, as cane blight directly affects the productivity of the fruiting wood. In severe cases, the entire cane may die back before the fruit matures.

Weakened plants are more susceptible to secondary infections and infestations by other pests, creating a cycle of decline within the raspberry patch.

If not managed correctly, the disease can spread rapidly through the entire plantation, necessitating the removal and destruction of affected sections or entire plants.

Initial symptoms typically appear in early summer as purple spots surrounding the leaf nodes. Over time, these lesions enlarge and may girdle the entire stem.

The center of the lesions becomes grey and develops numerous small black dots, which are the fungal pycnidia. The bark in these areas tends to crack and peel away.

As the disease progresses, the leaves on infected canes may yellow and drop prematurely. The canes become brittle, making them susceptible to wind damage and snapping under their own weight.

In humid conditions, a visible layer of fungal spores may be observed on the surface of the lesions. Infected buds often look shriveled and fail to break dormancy.

• Purple spots around the nodes of current-year canes.
• Bark splitting and cracking along the stems.
• Formation of small black dots (pycnidia) on the lesions.
• Premature leaf yellowing and dieback.
• Brittle stems that break easily under load.

The primary control measure is the immediate pruning and destruction of infected canes after harvest to reduce the primary inoculum load in the garden.

Maintain proper plant spacing to improve airflow and reduce humidity around the canes. Avoid excessive nitrogen fertilization that encourages overly succulent tissue growth.

Apply copper-based fungicides in the early spring before bud break to suppress fungal growth and protect the developing canes.

In cases of severe infestation, utilize systemic fungicides throughout the growing season, following a rotation program to prevent the development of fungal resistance.

Implement an integrated pest management strategy to control cane borers and midges, as these insects cause the physical damage that serves as entry points for the pathogen.