Informational table showing disease name, symptoms, pathogen/cause, and management of begonia diseases. Disease Symptoms Pathogen/Cause Management Bacterial Leaf Spot and Blight Water-soaked areas surrounded by yellow halos develop on leaves. Plants slowly die one leaf at a time. Xanthomonas campestris pv. begoniae Purchase plants free of the disease. Discard infected plants; particularly Rieger-types which are systemically infected. Remove infected leaves from Rex and tuberous types because they are not systemically infected. Do not wet leaves when irrigating. Do not propagate from infected plants. Destroy crop debris. Botrytis Blight Cuttings rot at their base. Tan spots develop on leaves. Established plants rot at the crown. Infected tissue is covered with dusty gray fungal growth. Botrytis cinerea Maintain low humidity by spacing plants and venting to improve air circulation. Remove dead and dying flowers and leaves. Apply a fungicide to protect plants. Foliar Nematode "Plants are stunted. Excessive red pigment develops in infected leaves. Bronzed or water-soaked areas develop on leaves of some cultivars. Fibrous rooted cultivars have small brown leaf spots.Some cultivars exhibit no symptoms despite heavy infection. Aphelenchoides fragariae Purchase nematode-free plants. Avoid overhead irrigation and splashing. Discard infected plants. Powdery Mildew White, mealy fungal growth develops on leaves, flowers, and stems. Tissue beneath the fungus may die. Oidium Examine plants carefully and frequently to detect the onset of disease. Maintain a fungicide program to protect plants. Apply a fungicide to protect plants. Pythium Rot Seedlings die. Shiny blackened areas develop on the stems and petioles of established on the stems and petioles of established plants at and just above the soil line as plants collapse and die. Pythium Plant in pasteurized potting media. Keep hose ends off the ground. Do not overwater. Apply a fungicide to protect plants. Rhizoctonia Crown Rot "Stems rot at the soil line. Plants collapse and die.A fine webbing of fungal growth may be seen between the infected stems and nearby soil particles." Rhizoctonia Plant in pasteurized potting media. Apply a fungicide to protect plants. Viruses Mosaic, malformed leaves, pale yellow ring spots, severe chlorotic mottling of leaves or plant stunting may occur. Impatients necrotic spot, tobacco ring spot, broadbean wilt, cucumber mosaic, tobacco necrosis virus. Purchase plants free of symptoms. Discard infected plants. Plant in pasteurized potting media. Maintain good aphid and thrips control to reduce spread.