Phyllosticta leaf spot of cranberry

Phyllosticta leaf spot and fruit rot is a fungal disease affecting cranberry plants, caused by the pathogen Botryosphaeria vaccinii (anamorph Phyllosticta elongata). This pathogen is known to reduce plant vigor and can lead to significant losses in berry yield if left unmanaged.

The fungus survives the winter primarily in infected leaf litter and stem tissues. As the growing season progresses, the fungus produces spores that are dispersed by water splashes, wind, and agricultural equipment. This cycle allows the disease to persist in fields and spread rapidly under favorable conditions.

Symptoms typically include small, grayish-brown spots on the leaves, often surrounded by a dark brown or black margin. On the berries, the infection results in distinct sunken lesions. As these lesions expand, they cause the fruit to soften, collapse, and eventually mummify, rendering the crop unmarketable.

Environmental conditions play a crucial role in the development of the disease. High humidity, frequent rainfall, and stagnant air within the cranberry canopy are major drivers for spore germination and infection. Dense plantings that prevent proper drying of the foliage are particularly susceptible to severe outbreaks.

Integrated pest management strategies are essential for controlling the disease. Key practices include:

• Maintaining proper spacing to ensure airflow.
• Sanitation, including the removal of dead plant material.
• Monitoring fields during critical growth stages.
• Applying registered fungicides during bloom and early berry development.