Double spot of cranberry

Double spot, caused by the fungal pathogen Dothichiza caroliniana, is a destructive foliar disease affecting cranberry plantations. The fungus attacks the leaves, leading to chlorosis, tissue necrosis, and premature defoliation, which severely impacts the overall vigor and productivity of the berry crop.

The primary host for this pathogen is the cranberry. The fungus spreads through the movement of spores, usually facilitated by rain splashes or overhead irrigation systems, which transfer the inoculum from infected leaves to healthy ones, creating new infection sites throughout the growing season.

Symptoms are identified by the appearance of distinctive lesions on the leaf surface. These spots often feature a unique appearance with a central necrotic area surrounded by a defined, darker border, giving the impression of a double-layered structure. As the infection progresses, these spots can coalesce, leading to significant leaf damage.

Developmental conditions for the disease include prolonged periods of high humidity, moderate temperatures, and poor air circulation within the plant canopy. Since Dothichiza caroliniana survives the winter in fallen leaves and debris, sanitation is a critical component in managing the spread of the fungus in subsequent years.

To effectively manage and prevent double spot, growers should implement the following agricultural practices:

• Remove and destroy all leaf litter from the field to reduce the initial inoculum level.
• Apply preventative fungicide treatments during the spring and summer as recommended by local guidelines.
• Maintain adequate plant spacing to promote better airflow and reduce leaf wetness duration.
• Monitor the plantation regularly, focusing on the lower canopy where moisture often accumulates.