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Scab, Sunburn and Salt Injury
Symptoms of scab are rather varied; however, it usually appears first as a tiny, water-soaked, and often raised area on the underside of the leaf. These spots enlarge and may become corky, brown in color, and of irregular size and shape. The condition may also appear on the top of the leaf.
Scab is a physiological condition associated with excess moisture or fluctuations of moisture from too high to too low. There is no biological agent associated with this condition and chemical sprays are ineffective. It is believed that improvement of drainage and growing conditions are the best possible controls.
Sunburn or sunscald appears as yellowish or bronzed areas on the upper side of the leaves with severely affected areas turning brown. These brown areas nearly always are interveinal and appear in the center of the leaves as opposed to salt injury which appears at the leaf margins. It is especially seen on plants with virus variegation in the foliage or when plants are moved from shade to sunshine. Some varieties are more susceptible than others.
Salt injury is characterized by browning and death of the leaf tissue beginning at the margins and progressing inward. Most often the injury will appear first on older leaves
Too high a concentration of salts in the soil or in the irrigation water or the use of heavy doses of fertilizer coupled with inadequate irrigation will cause this condition. This problem will develop rapidly in container grown plants.
To prevent this condition, camellias should be planted in a medium with good drainage. An occasional heavy irrigation will help to leach away the excess salts.