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Camellia Flower/Petal Blight
Camellia flower or petal blight, caused by the fungus, Ciborinia camelliae Kohn, is a disease affecting flowers of camellia only, but not roots, stems, or leaves. Symptoms include brown spots of the petals and sometimes of stamens and calyx. These spots, which begin as small brown specks, enlarge rapidly during warm weather as the fungus invades and kills flower tissue. A gray fuzzy growth may be observed at the base of the flower where it attaches to the stem. Eventually the fungus invades to the flower base where a hard, black structure called a sclerotium forms. It is only by this structure that the fungus survives from season to season. This fungus does not spread from flower to flower, as in the case of azalea petal blight, a disease caused by a related fungus. The fungus attacks only camellia flowers, but not other flowers that may be in bloom at the same time. Symptoms of the disease are not observed in the fall but may be seen as early as December in very warm climates or as late as February or March in cooler climates.
This fungal body, the sclerotium, lies dormant and remains viable on, or in, the soil for one to five years or more. The time of germination, however, is variable. A period of cool weather followed by warmer temperatures and moisture is required for germination. Factors, such as temperature and moisture may allow it to germinate and develop under warm, moist conditions, but when soils are dry or temperatures are low (about 45 °F or lower) it remains quiescent until favorable conditions prevail. As the sclerotium germinates it sends up a stipe (stalk) until it reaches light, at which time the stalk ceases to elongate and at that time forms a tan, saucer-shaped structure (called an apothecium). This apothecium resembles a very small mushroom. At the maturity of the apothecium, spores are forcefully discharged into the air and become windblown. If a spore or spores fall on a camellia flower, they germinate and penetrate the petal tissue and, depending on temperature, brownish spots develop where the fungal spores penetrated. As the fungus advances in flower tissue, the spots enlarge, usually being circular in shape, often growing toward the center of the flower.
This disease will spread for short distances by windblown spores of the fungus. Long distance spread is through the moving of plants with infested soil from one location or another. The fungus may also be spread by the distribution of diseased flowers.
As far as is known, all camellia species and varieties are susceptible, but small differences are noted. This may be because of flower structure or some unknown factor, or it just may be that not many spores reach certain plants because of location. Infection of Camellia sasanquas is not seen due to their early period of bloom rather than any resistance to the fungus causing flower blight.
The best control method for camellia flower blight is to keep the fungus out (exclusion). If the disease has not become established in an area, extreme caution should be taken to prevent its introduction. Quarantine was established as an early method of control in the 1950's to prevent the spread of this disease. However, it was unsuccessful as this disease has become established in almost all camellia growing areas in the United States. Picking up diseased flowers, including single petals and those lodged in branches, helps to control this disease if all neighbors cooperate or if you are located in an isolated area. All flowers should be destroyed by burning or sending them with the garbage to landfills. Do NOT put in compost as these sclerotia will survive. Chemical applications as control measures have been disappointing although azalea flower blight has been successfully controlled in this way. Since camellia plants flower over a long period of time as opposed to the mass bloom of azaleas numerous applications of fungicide may be necessary to obtain any control. The application of systemic fungicides to flower buds before opening has been unsuccessful as a protectant against this disease.
One of the better methods of control is to raise fall-flowering camellias or to grow camellia varieties that respond to the applications of gibberellic acid causing them to flower in the fall months when the fungus is not active.
The American Camellia Society is continuing to encourage new research to discover better methods of control for this disease that has plagued camellia growers for over forty years.