Exobasidium leaf spot of bearberry

Pathogen and disease type. The disease known as bearberry leaf spot is caused by the fungus Exobasidium uva-ursi. This is a basidiomycete pathogen that causes hypertrophy, leading to the formation of galls and deformations on the plant's leaves. It acts as an obligate parasite that interferes with the plant's normal physiological functions.

Host plants. The primary and specific host for this fungus is the bearberry (Arctostaphylos uva-ursi). The disease is frequently observed in wild populations, where it affects the quality of the foliage, making the plant unsuitable for harvesting and medicinal use due to the structural damage caused by the fungus.

Symptoms and signs. The characteristic symptoms include the development of swollen areas or galls on leaves, often turning bright red or pink. These lesions can result in the twisting or curling of the leaf blades. A white, powdery layer may appear on the undersides of the affected leaves during the sporulation phase, indicating the active release of fungal spores.

Conditions for development and spread. Exobasidium uva-ursi thrives in environments characterized by high humidity, cool temperatures, and frequent rainfall. The spread is facilitated by wind and splashing water, which distribute spores from infected tissues to healthy leaves. Densely growing plants with poor air circulation are particularly susceptible to severe outbreaks.

Control and prevention measures. Management strategies mainly focus on sanitation in areas where bearberry is harvested.

• Regularly remove and destroy symptomatic leaves and shoots.
• Improve air circulation around plant stands to reduce humidity.
• Avoid harvesting from heavily infested areas to prevent further spread.