Snapdragon (Antirrhinum) Diseases
Gary W. Moorman, Professor of Plant Pathology
|ANTHRACNOSE||Definite yellow spots form on leaves and stems. These turn white and have a brown border. Leaves die as do entire plants if stems are girdled.||Colletotrichum antirrhini||Heat and ventilate to maintain low humidity. Water in a manner that keeps foliage surfaces dry. Apply a fungicide to protect healthy plants.|
|BOTRYTIS BLIGHT||Petals turn brown and are covered with gray, fungal growth.||Botrytis cinerea||Space plants to insure good air circulation. Maintain low humidity. Avoid watering late in the day. Remove crop debris. Apply a fungicide.|
|DOWNY MILDEW||Seedlings and cuttings are stunted and leaves curl downward. Gray to white fungus lightly covers the underside of leaves. Upper side of infected leaves have yellowed areas. The fungus causes a systemic infection of all leaves of seedlings. Older plants yellow, may be stunted, and die from the top down. Plants fail to flower.||Peronospora antirrhini||Heat and vent to maintain low humidity, especially when weather is cool and cloudy. Water in a manner that keeps leaf surfaces dry. Apply a fungicide. Before replanting greenhouse beds, steam the soil because the fungus survives in debris.|
|POWDERY MILDEW||White fungal growth forms on either surface of lower leaves, also on stems of some cultivars.||Oidium spp.||Heat and ventilate especially in the spring and fall to reduce night humidity. Apply a fungicide.|
|PYTHIUM ROOT ROT||Root tips turn brown and die. Plants are yellowed, stunted, wilt, and die. Older plants may survive if not placed under moisture stress.||Pythium spp.||Plant in pasteurized raised beds. Do not recontaminate beds. Apply a fungicide to protect healthy plants.|
|RHIZOCTONIA STEM ROT||Stems of seedlings or recent transplants collapse at the soil line. A red-brown lesion forms at the base of the stem. Older plants wilt and die with lesions at the base as noted above.||Rhizoctonia solani||Plant in pasteurized raised beds. Apply a fungicide to protect healthy plants.|
|RUST||Small yellow swellings form on leaves or stems and burst to release rusty colored spores. Concentric rings of spores form around the initial spot.||Puccinia antirrhini||Apply a fungicide to protect healthy plants.|
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