Camellia Canker and Dieback
Camellia Canker and Dieback
Camellia canker and dieback is a serious disease in the Southeast and along the Gulf Coast where temperatures and humidity remain high throughout much of the year. It is quite well known by camellia growers in the Deep South and is particularly severe on camellias grown in heated greenhouses.
Camellia CankerThe fungus that causes this disease, Glomerella cingulata, grows well where weather conditions are hot and humid. The disease attacks C. sasanqua, C. reticulata, and C. hybrids more severely than C. japonica, although it causes damage and plant death among all of the camellia species. Some varieties are much more susceptible to this disease than others.
Most camellia cultivars developed through the years by camellia enthusiasts have been selected for flower characteristics such as color, size, and bloom season with little attention given to selection for disease resistance. Only the extremely susceptible varieties have been eliminated due to the difficulty of growing and propagating these plants.
Symptoms of the disease are seen as cankers on stems or dieback of twigs and branches. The first plant symptom usually observed is wilting and death of small, current season twigs. On very young tissue, the leaves fall off leaving a naked twig after wilting and death have occurred. With older twigs, death may occur suddenly but the leaves turn brown and do not fall off. The wood at the base of these twigs is dead and discolored in appearance if the bark is scraped off. This apparently prevents the movement of water from the stem to the twig thus causing wilting and death.
The fungus continues to destroy the adjacent wood tissue while the surrounding healthy wood continues to grow, thereby enlarging the stem diameter. This area of dead cells appears to be sunken since there is no new growth of the stem, resulting in a canker. The canker, composed of this area of dead wood, provides the food base for the fungus so that it may survive from season to season and reproduce by producing millions of spores. If cankers form on the main trunk of the plant, this disease may eventually cause the death of the entire plant.
Camellia DiebackThe fungus causing this disease must enter susceptible camellia tissue through wounds. The fungus may enter through a leaf-scar in the spring during the time of camellia leaf-fall. Other points of entry may include wounds caused by pruning, lawn mower injury, etc. On C. sasanqua plants the fungus may enter the stem where a leaf gall has occurred. These leaf galls are fairly common in the spring as new growth begins. The disease may also be a problem on grafted plants, entering the grafting wound. Infrequently, the fungus will penetrate non-wounded young leaves forming a circular spot. This phase of the disease is usually seen only under very crowded and wet conditions and is of minor importance.
The fungal spores of this disease are usually spread by splashing water, either rainfall or irrigation. The fungus may spread easily in the greenhouse where plants are generally placed close together. Infrequently, insects such as ants may carry the fungal spores from one plant to another. Long distance spread of the disease is through the moving of infected plants from one area to another.
Control of Canker and DiebackControl of this disease should be attempted through a combination of chemical and cultural methods. Fungicides should be used during the spring at leaf drop to prevent spread of this disease. These fungicides will act as a protectant against the fungus but will not cure the disease after infection has occurred.
Fungicides should also be sprayed following pruning, especially during the spring when temperature and moisture is ideal for the fungus. Before grafting, scions should be soaked in a fungicide solution for an hour as a protection against this disease. Cuttings should also be soaked before inserting in the rooting medium.
Sanitation is a good method of disease control. All dead or dying material should be pruned off immediately and destroyed to prevent further spread to other plants. Pruning of plants to allow for good air circulation throughout the plant and proper spacing of camellias will help to reduce the incidence of disease. Avoid excessive applications of nitrogen as tender new growth is more susceptible to the fungus than that which has hardened. Infected plants should be removed from healthy plants to prevent spread of the disease.
The formula for a fungal control bleach mixture is 1 part bleach to 10 parts of water.