Exobasidium blight of cranberry

Exobasidium blight, caused by the fungus Exobasidium oxycocci, is a significant fungal disease affecting cranberry crops. This pathogen specializes in parasitizing cranberry plants, leading to severe morphological abnormalities in their growth. The disease is known to impact both wild patches and cultivated cranberry bogs, making it a critical concern for agricultural health.

The primary symptom of the infection is the hypertrophy and discoloration of the cranberry plant tissue. Infected shoots become thickened, deformed, and often develop a rosette appearance, which is frequently described as a «witches' broom» effect. The leaves on these shoots may turn pale green, yellow, or take on a distinct reddish or pinkish hue, signalling the presence of the pathogen.

Under favorable environmental conditions, a white or pinkish powdery layer of spores appears on the surface of the deformed plant parts. This is the reproductive stage of the fungus, which allows the pathogen to spread efficiently to adjacent healthy plants via wind, water splashes, or even through tools used for field maintenance. If left untreated, the affected shoots eventually wither and die.

The development of Exobasidium oxycocci is heavily dependent on moisture and humidity. High humidity levels, combined with cool temperatures, create an ideal environment for the spores to germinate and infect new tissue. Stagnant water and poor ventilation within the cranberry bed are key factors that promote the rapid spread of the disease across the field.

Effective management and prevention strategies are essential for maintaining crop yield. Key practices include:

• Strict sanitation by pruning and removing symptomatic shoots from the field.
• Implementing proper water management to prevent excessive moisture build-up.
• Applying fungicides during the early spring period to suppress fungal growth.
• Regular inspection of the bog to catch the disease in the early stages of development.