Question: The leaves of my plant have gone yellow. What has caused this?
This symptom can have many different causes. Root problems can again be responsible, but if the yellowing is confined to the areas between the veins, then the problem is most likely to be a nutrient deficiency. Being ericaceous (acid-loving) plants, camellias can suffer from iron and manganese deficiencies if the soil or growing medium is too alkaline. In gardens with alkaline soils they are best grown in containers using an ericaceous compost. Use acidic fertilisers, and avoid prolonged watering with tap water if you are in a hard water area. Chelated iron and other trace elements will allow camellia to take up nutrients in alkaline soils although effective chelated fertilisers are expensive and annual treatments are needed. 'Sequestrine' is a common trade name for chelated fertiliser.
Irregular yellow or creamy-white blotches on the leaves may be the result of infection by Camellia yellow mottle virus. This virus has little effect on plant vigour.
Although they are evergreen plants, camellias still periodically shed their old leaves. Don’t worry about leaves turning yellow and falling in spring or summer if this is confined to old leaves near the base and within the plant.
Question: Some of the leaves of my plant have turned brown. What is the problem?
Again, there can be a number of causes for this, such as a root problem, drought, frost damage or strong winds. Affected leaves may be shed.
If the browning takes the form of spots or blotches, then it is possible that the plant has become infected with one of the leaf blight fungi. It is sometimes possible to see small, black, fruiting bodies of the causal fungus within the affected area. In severe cases the pathogen can progress into the branch to cause dieback.
Question: Many of the leaves of my camellia have a thick, black growth on the surface. What has caused this?
The black growth is that of a sooty mould fungus. This grows on the sugary honeydew excreted by sap-sucking pests, and on camellia the usual source of the honeydew is an infestation by cushion scale. Check the underside of the leaves for small, light brown scales, often with an elongate white egg sac. Sooty mould is not directly harmful to the plant and can be washed from the leaves, but unless the pest is controlled the growth will reappear.
Question: My plant looks healthy apart from one or two leaves, which became very swollen and have now turned white. Is this a significant problem?
Your plant is affected by a fungal disease called camellia gall. Whilst unsightly, this is not a serious problem. Affected parts can be picked off, ideally before the white bloom of fungal spores is produced.
Question: The leaves of my camellia have raised corky spots and patches underneath. What has caused this?
It sounds as though the leaves could be affected by oedema. This is not a pest or disease but a physiological problem, caused when the plant takes up more water through its roots that it can lose readily through the leaves. Overwatering or waterlogging can be to blame, or occasionally camellias grown in polytunnels or under glass where humidity is high can exhibit problems of oedema.