Exobasidium perenne

The causal agent of this disease is the fungus Exobasidium perenne, a parasitic basidiomycete. It is a specialized pathogen that primarily targets the genus Vaccinium, specifically lingonberries (Vaccinium vitis-idaea), causing significant structural changes in the host plant tissues.

The disease affects vegetative growth, leading to hypertrophy where the fungus triggers abnormal cell division. This parasitic relationship is long-term, as the fungus often colonizes perennial parts of the shrub, allowing it to survive through winter and reappear in the same locations year after year.

Key symptoms include fleshy, thickened, and distorted shoots and leaves, which often appear pale pink or white due to the development of fungal mycelia. A distinct white, mealy layer forms on the undersides of the leaves or on the shoots; this is the reproductive stage, consisting of basidia that release spores for further infection.

The spread of Exobasidium perenne is highly dependent on environmental factors, particularly high humidity, rain, and cool temperatures during the early growing season. Spores are easily disseminated via wind currents or rain splashes, facilitating rapid secondary infections across commercial or wild patches of lingonberries.

The impact on agriculture is significant, as the infection reduces plant vigor, damages foliage, and limits berry production. Effective management strategies include:

• physical removal and destruction of infected plant parts;
• maintaining proper plant spacing to improve air circulation;
• applying copper-based fungicides during the early bud-break stage;
• improving field drainage to prevent localized humidity spikes.