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Snapdragon (Antirrhinum) Diseases

Informational table showing disease name, symptoms, pathogen/cause, and management of Snapdragon (Antirrhinum) diseases.
Disease Symptoms Pathogen/Cause Management
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.

Anthracnose
Anthracnose.

Downy mildew
Downy mildew.

Rust
Rust.

Prepared by Gary W. Moorman, Professor of Plant Pathology

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Snapdragon (Antirrhinum) Diseases

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