Cladosporium ossifragi infection

Cladosporium ossifragi is a fungal pathogen that primarily affects the cloudberry (Rubus chamaemorus) and other related species in northern latitudes. It is known to cause a destructive disease, often referred to as the 'bone-breaker' fungus due to the way it consumes and destroys the internal structures of the berry fruits.

The causal agent is a specialized fungus that thrives in the humid conditions of tundra ecosystems. Unlike generalist species of Cladosporium, this specific pathogen focuses on the generative organs of the host plant. It colonizes the ovaries and developing fruits, causing significant physiological damage that leads to total crop loss if conditions are ideal for the fungus.

Symptoms begin as a slight discoloration on the surface of the fruit, followed by the appearance of an olive-brown mold. As the disease progresses, the berries turn completely black, become desiccated, and essentially mummify. The fungus breaks down the internal matrix of the berry, making it inedible and worthless for harvest.

The development of the fungus is strictly governed by climate. High humidity and cool, damp weather patterns are the primary drivers of spore dispersal and infection rates. Because the fungus survives on dead vegetation and in soil debris, it effectively maintains its presence from season to season, ready to attack during the next flowering window.

Integrated pest management strategies are crucial for mitigation. Key actions include:

• Removal and destruction of all infected plant materials after the season to reduce the inoculum.
• Application of targeted fungicides during critical growth stages when high humidity is predicted.
• Cultural practices that favor good air circulation around the plants to reduce surface moisture.
• Site selection ensuring proper drainage to prevent water accumulation near the base of the plants.