Algal spot, also called green scurf, is caused by algae (Cephaleuros virescens) that are common on camellias and other ornamentals in the South. During moist weather, cells of the algae enter the leaves or twigs and spread rapidly. The invaded twig tissue may swell and crack. If the crack encircles the twig, the twig dies. The infected camellia leaves turn greenish brown at first. If the algae develop spore-producing bodies (tiny, round heads on fine, dense, reddish hairs) the patches appear reddish brown and velvety or cushiony. The algae spread rapidly when rains are frequent and heavy. Camellia plants weakened by poor growing conditions are most susceptible to algal spot.
Control measures are rarely necessary. If plants are weak, water and fertilize regularly. Prune dead twigs. Improve air circulation around camellia plants by thinning out nearby dense vegetation.
This serious and widespread plant disease is caused by a fungus (Ciborinia camelliae) that attacks only the flowers of camellias. In late winter to early spring, black fungal resting structures in the soil produce spores that are carried by the wind to new flowers. If moisture is present, the spores germinate and cause infection. The flowers may turn completely brown within 48 hours. The fungus continues to grow in the flower, eventually producing black resting structures that drop from the shrub with the flower. These resting structures can persist in the soil for at least 5 years.
Remove and destroy spent flowers to eliminate the source of new infections the following spring. Rake up and destroy old leaves, flowers, and plant debris. Apply a fungicide labeled for camelia flower blight, fllowing label directions.
This plant disease is caused by a fungus (Exobasidium camelliae) found only on camellias in the Southeast. The disease is more common on Sasanqua varieties than on Japonica. As the buds open in spring, fungal spores blown by wind to the plant or overwintering on the bark enter the tissue. The spores need moisture to germinate. Plants grown in areas of poor air movement or in deep shade where moisture levels are high are most likely to be infected.
Fungicides are seldom necessary in home gardens. Remove all galls before the white powdery growth appears. If the galls are not removed and destroyed, the disease will be more severe the following year. If practical, move the plant to an area with better air circulation, and avoid planting camellias in deep shade.
This is a common problem in acid-loving plants such as camellia. The plant prefers soil with a pH between 5.5 and 6.5. The soil is seldom deficient in iron, but iron is often found in an insoluble form that is not available to the plant, especially in soil with a pH above 7.0. A high soil pH can result from overliming or from lime leached from cement or brick. Regions where soil is derived from limestone or where rainfall is low also have high-pH soils. Plants use iron in the formation of chlorophyll in the leaves. When iron is lacking, new leaves are yellow.
Treat the soil with aluminum sulfate, watering it in well. Fertilize with plant food for acid-loving plants. When planting camellia, add enough peat moss to make up at least 50 percent of the amended soil if you live in an area with poor drainage. Never lime the soil around camellia.
Many species of scales infest camellias. They lay their eggs on leaves or bark, and in spring to midsummer the young scales, called crawlers, settle on various parts of the shrub. These small (1/10 inch), soft-bodied young feed by sucking sap from the plant. The legs usually atrophy, and a hard crusty or waxy shell develops over the body. Mature female scales lay their eggs underneath their shells. Some species of scales that infest camellias are unable to digest all the sugar in the plant sap, and they excrete the excess in a fluid called honeydew. A sooty mold fungus may develop on the honeydew. An uncontrolled infestation of scales may kill the plant after two or three seasons.
Apply a horticultural oil or an insecticide labeled for scales, following label directions.
This common black mold is caused by several species of fungi that grow on the sugary material left on plants by aphids, mealybugs, scales, whiteflies, and other insects that suck sap from the plant. The insects are unable to digest all the sugar in the sap, and they excrete the excess in a fluid called honeydew, which drops onto the leaves below. The honeydew may also drop out of infested trees and shrubs onto camellias growing beneath them. Sooty mold is unsightly but is fairly harmless because it does not attack the leaf directly. Extremely heavy infestations prevent light from reaching the leaf, so the leaf produces fewer nutrients and may turn yellow. The presence of sooty mold indicates that the camellia or another plant near it is infested with insects.
Hose off sooty mold or wipe it from the leaves with a wet rag. Rain will eventually wash it off. Prevent more sooty mold from growing by controlling the insect that is producing the honeydew. Inspect the leaves and twigs above the sooty mold to find out what type of insect is present.