Branch and collar canker (<i>Phomopsis theae</i>)
The first obvious symptom of attack is yellow or brown foliage on affected branches or bushes, contrasting with the green foliage of the surrounding healthy bushes. Closer examination reveals lesions or cankers at the base of branches or at the collar region of the bush. These lesions are less apparent in the early stages of infection but older cankers are easily recognisable by their raised margins due to the development of callus.
The diseased areas may be regular or irregular in shape, often sunken, and grey to black in colour. The underlying dead wood can be seen by scraping back the bark using a knife. In instances where the branch or the collar is completely girdled (ring-barked), a thick ridge of callus forms at the upper margin of the canker. The fungus can also infect apparently uninjured succulent green shoots, causing small local lesions. This can lead to the death of the whole shoot. Tea plants are most susceptible when they are less than 8 years old.
The disease is enhanced by drought conditions, deep planting, planting in gravelly soils, mulching close to the collar, wounds by weeding implements, low moisture status in the bark and surface watering during dry weather.
- Use resistant varieties, if available, particularly in areas with a history of the disease.
- Plant only healthy, vigorous plants with a well-developed root system.
- Avoid planting in poor soils and in areas where rainfall is marginal or inadequate.
- Mulch the soil towards the end of the rainy season to prevent it drying out too quickly.
- Plants should be treated lightly (light plucking) during propagation and nurturing.