Disease

Anthracnose Sunken black spots appear on the foliage of Palms, Ficus, and other susceptible plants. Dark brown streaks may occur at the leaf tips. This disease is associated with warm and very moist conditions, and it is therefore much more likely in the greenhouse than in the living room. Remove and burn infected leaves, spray the plant with systemic fungicide and keep it on the dry side without misting for serveral weeks.		Black Leg A disease of stem cuttings, especially Petargonium. The base of the cutting turns black, due to the invasion of the Botrytis fungus. Remove the infected cutting as soon as possible. The cause is overwatering or overcompaction of the compost which has prevented proper drainage. Make sure that the Seed and Cutting Compost is kept drier next time you take Pelarginium cuttings; do not cover with glass or polythene.
Botrytis (Grey Mould) Familiar grey, fluffy mould which can cover all parts of the plant -- leaves, stems, buds, and flowers if the growing conditions are cool, humid, and still. All soft-leaved plants can be affected -- Begonia, Cyclamen, Gloxinia, and Saintpaulia are particularly susceptible. Cut away and destroy all affected parts. Remove mouldy compost. Spray with systemic fungicide. Reduce watering and misting; improve ventilation.		Crown and Stem Rot Part of the stem or crown has turned soft and rotten. When the diseased area is at the base of the plant it is known as basal rot. The fungus usually spreads rapidly and kills the plant -- the usual course is to throw the pot, compost, and plant away. If you have caught the trouble early, you can try to save it by cutting away all diseased tissue. In future avoid overwatering, underventilating, and keeping the plant too cool.
Damping Off The damping off fungi attack the root and stem bases of seedlings. Shrinkage and rot occur at ground level and the plants topple over. The golden rules are to use sterilized compost, sow thinly, and never overwater. At the first sign of attack remove collapsed seedlings, improve the ventilation and move the seedlings to a cooler spot. Water the remainder with Cheshunt Compound.		Leaf Spot Brown, moist spots appear on the foliage of Citrus, Dracaena, Dieffenbachia and other susceptible plants. In a bad attack the small spots enlarge and merge, killing the whole leaf. Both bacteria and fungi can cause this effect -- the best general treatment is to remove and burn infected leaves, spray the plant with systemic fungicide and keep it on the dry side without misting for several weeks.
Oedema (Corky Scab) Hard corky growths sometimes appear on the underside of leaves. this disease is not caused by either a fungus or bacterium; it is the plant's response to waterlogged compost coupled with low light intensity. Badly affected leaves will not recover so they should be removed. Transferring the plant to a better lit spot and reducing the frequency of watering will result in healthy new foliage.		Powdery Mildew A fungus disease which grows on the surface of leaves, spotting or coating them with a white powdery deposit. Unlike Botrytis this complaint is neither common nor fatal, but it is disfiguring and can sprread to stems and flowers. Remove badly mildewed leaves and spray the plants with systemic fungicide or dinocap. Alternatively, lightly dust the leaves with sulphur. Improve ventilation around the plants.
Root Rot A killer disease to which Cacti, Succulents, Begonia, Palms, and Saintpaulia are particularly prone. The first sign is usually the yellowing and wilting of the leaves which is rapidly followed by browning and collapse. The cause is fungal decay of the roots due to waterlogging and you can only save the plant if the trouble is spotted in time and you follow perform Root Rot Surgery.		Rust An uncommon disease which need not concern the ordinary houseplant owner. The only plant you are likely to see infected with rust is the Pelargonium -- brown concentric rings of spores on the underside of the leaves. It is difficult to control -- remove and burn infected leaves, improve the ventilation around the plants and spray with mancozeb. Do not propagate cuttings infected with this disease.
Sooty Mould A black fungus which grows on the sticky honeydew which is deposited by aphid, scale, whitefly, and mealy bug. The unsightly mould does not directly harm the plant, but it does reduce growth and vigour by blocking the pores and shading the surface from sunlight. Remove sooty mould by wiping with a damp cloth; rinse with clean warm water. Control future attacks by spraying promptly against the pests which produce honeydew.		Virus There is no single symptom of virus infection. The growth may be severely stunted and stems are often distorted. The usual effect on leaves is the appearance of pale green or yellow spots or small patches. Coloured flowers may bear large white streaks. The infection was brought in by insects or was already present in the plant at the time of purchase. There is no cure -- throw away the plant if you are sure of your diagnosis.