American Camellia Society Camellia Growing Tips & Culture
American Camellia Society The Garden Report: Questions & Answers
Norfolk Botanical Garden Hofheimer Camellia Garden
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Camellias are healthy plants with few problems when compared to cultivated crops such as tomatoes, apples, and peaches. However, several disease problems may occur on camellias. Root rot and dieback are the two more important diseases that can result in death to the plants. Flower blight is also a serious problem as it disfigures the bloom, but it does not cause death or decline of the plant.
Dieback: Dieback is a serious disease of both C. japonica and C. sasanqua caused by the fungus Glorerella cingulata. This fungus usually requires a wound to enter the plant. Leaf scars, hail injury and wounds created from lawn mowers, pruning cuts, falling branches and insects are points of entry for the fungus. The fungus may be spread by insects that walk across wounds or by splashing rain or water. Spread of the disease is usually during the spring and early summer months.
The disease is characterized by sudden wilting of new growth, particularly in early summer. The leaves characteristically cling to the branches for a considerable length of time after they die. Cankers can sometimes be seen at the infection point, and these may ooze pink masses of fungal spores during extended periods of wet weather.
The best control of dieback is sanitation. The fungus lives inside the plant and cannot be completely controlled by spray. Diseased branches should be removed about 6 inches below the lowest visible symptom of disease. Pruning tools should be dipped in a solution of fungicide or bleach and water between each cut if infection is suspected. All wounds should be sprayed with this solution. This diseased twigs should be burned or physically removed. Spraying of plants with a fungicidal solution in the spring during the normal leaf-fall period will help to prevent the spread of the fungus.
Root rot: Camellia root rot is caused by a fungus (Phytophthora cinnamomi) which occurs in the soil. This pathogen may be found occurring naturally in the soil or it may be brought in on the roots of camellias, rhododendrons, and other woody ornamentals. Most Camellia japonica varieties are susceptible to root rot, while Camellia sasanqua and Camellia oleifera are not as susceptible.
Root rot is usually associated with poorly aerated or poorly drained soils. Symptoms may appear at any time, but they often show up during periods of hot, dry weather. The first sign of this disease is the stopping of growth either with or without yellowing. In more advanced stages the leaves on one or more branches become gray-green, wilt, and finally die. Plants infected with root rot are unable to take up water and will eventually die from lack of water. If the roots are examined they are brown with rot.
Three approaches to control exist: 1) use C. sasanqua and C. oleifera as understock for grafting. This gives some protection; 2) use vigorous fast-growing varieties; 3) use a fungicide as a soil treatment. This is expensive and may not completely rid the soil of the fungus. Most important, however, is to do whatever is necessary to improve drainage of the soil.
Camellia flower blight: This disease of camellia caused by the fungus Ciborinia camelliae occurs only on the flower and does not affect the rest of the plant in any way. Since camellias are enjoyed mainly for their flower, this can be a very devastating disease.
Flower blight is not usually a problem early in the season. It generally appears in late winter to early spring when the temperatures are on the rise. However, it may be seen earlier if conditions are proper for the fungus. Warm, humid weather following a cold spell will cause sporulation of the fungus and subsequent infection. This disease is characterized by brown spots on the petals. These usually enlarge until the entire blossom is blighted. Infected flower tissue feels "slimy" to the touch.
Infected flowers fall to the ground and the fungus produces hard, resting bodies called sclerotia. These sclerotia may remain under the bush or in the soil or debris for several years. Under proper weather conditions (temperatures from 45 - 70° F, wet) these sclerotia germinate and develop saucer-shaped mushrooms (apothecia) about 1/2 inch in diameter that release spores. These spores are carried by the wind and cause infection when they land on a flower.
Control measures involve the removal and destruction of all fallen blossoms. If all flowers could be picked up every year this would disrupt the life cycle of the fungus. However, this is only effective if you do not live close to other camellia growers as the fungal spores may easily blow from yard to yard. If flower blight has not been found in an area, it is important not to bring flowers or infected soil on plants into this area. Protective fungicidal spray have only provided limited protection. At this point, eradication is not truly possible although investigation of various control methods continues. Some fungicidal sprays, such as Bayleton, applied weekly will reduce disease incidence but not eliminate it.
Other diseases: Other diseases of camellia include leaf gall, sooty mold, lichens, nematodes, and virus variegation. None of these are usually life threatening. For more information contact the American Camellia Society horticulturist.
The American Camellia Society publishes Camellia Diseases, a leaflet of more information that is illustrated with color photographs. Please email the ACS gift shop for ordering information for Camellia Diseases, item 4206/Diseases.
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