EXOBASIDIUM CAMELLIAE

Exobasidium camelliae is a pathogenic fungus that causes a specific disease known as leaf gall or blister on camellia plants. This pathogen belongs to the Exobasidiaceae family and is a significant concern for both professional nurseries and hobbyist collectors who grow Camellia japonica and Camellia sasanqua species.

The fungus primarily targets the tender growth of the plant, including developing leaves and shoots. By stimulating the plant cells, Exobasidium camelliae induces abnormal hypertrophy, resulting in swollen, fleshy tissue structures. If left untreated, the disease can significantly compromise the plant's aesthetic value and its vigor over several growing seasons.

Early symptoms include pale, thickened areas on the leaves. As the fungus progresses, these areas develop into prominent, distorted galls. Soon, the surface of these galls becomes covered with a white, powdery bloom, which consists of masses of fungal spores. As the season progresses, these galls turn brown, dry out, and lead to significant leaf drop, causing the plant to become sparse.

Environmental conditions are critical for the spread of this pathogen. The disease thrives in cool, humid environments with poor air circulation. Prolonged moisture on the leaves, whether from overhead watering or high humidity levels in greenhouses, facilitates the germination of spores and the subsequent infection of adjacent, healthy foliage.

Managing this fungal infection requires a multi-faceted approach centered on hygiene and environmental modification:

• Prune and remove all galls immediately upon detection before they release spores;
• Improve air circulation in the greenhouse or growing area to reduce humidity levels;
• Avoid overhead irrigation to keep the foliage as dry as possible;
• Apply preventative fungicidal sprays containing copper or other approved systemic agents during the early growth stage.