Camellia shrubs bloom in late autumn or late winter to early spring. Their large, colourful flowers liven up the landscape when most plants are waiting for spring to arrive. To keep camellias healthy, maintain a schedule of proper fertilising and watering practices. Regular maintenance can minimise or prevent camellia diseases.
Camellia flower blight is a fungal disease that affects only the flowers. The Ciborinia camelliae fungus lives in the soil and infects shrubs in the spring, when there is plenty of moisture from frequent rainfall. Flower blight begins in the centre of the flower as irregularly shaped, brown spots. It spreads over the flower quickly, turning the veins dark brown and can cause the flowers to fall off the shrub 24 to 48 hours after the first symptoms. Apply a fungicide containing triadimefon or mancozeb to reduce the impact of the fungal disease, if it is in the area. Keeping the area free of debris, laying fresh mulch around the base, not spraying water onto the shrubs or leaves, and leaving the mulch undisturbed can help lessen the chance of disease.
Another springtime camellia fungal disease is leaf gall. This disease commonly affects varieties of Camellia sasanqua, while Camellia japonica is rarely affected. The fungus Exobasidium camelliae infects new leaves and shoots as they open, making them thick and abnormally large. Infected foliage changes from light green to pink or almost white. The galls, bumps on the underside of the leaves, turn brown, harden and burst open releasing a mass of white spores. To keep the disease from spreading, remove all infected foliage as soon as the first symptoms appear, before the galls burst. Fungicide spray doesn't work on infected plants. Steps you can take to lessen the chances of infection include keeping water off the leaves during watering and removing debris around camellia plants.
If you have Japanese camellias, be on the look out for root rot. The sasanqua camellias are resistant to this fungal disease, which is caused by Phytophthora cinnamomi. Healthy camellias have white roots and small feeder roots. Shrubs with root rot have red-brown to dark-brown roots and no feeder roots. Other symptoms include poor shrub growth, yellow leaves and an overall wilting of the shrub. The fungus that infects camellias lives in warm soil that has poor drainage. Fungicides that contain mefenoxam and etridiazole prevent of root rot; they won't treat an already infected shrub.
The fungus Glomerella cingulata causes unsightly cankers -- sunken, rotted areas -- on the twigs and stems of camellia bushes. Canker symptoms typically appear during hot, dry weather, while death of the branches or branch tips occurs most often in the spring. The first symptoms to appear on young shrubs are yellow, wilting foliage, followed by grey areas on the stems. They grey areas turn into cankers, which may circle the entire stem. Older camellias can become infected, but dieback of the bush is slower. Prune stems about 7.5 cm (3 inches) away from the cankers so there is only healthy, live wood. Use fungicides containing copper salts of fatty acids or thiophanate-methyl during rainy periods and during the fall when leaves are dropping.