Snapdragon (Antirrhinum) Diseases
|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.|
||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.|
||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.|
Prepared by Gary W. Moorman, Professor of Plant Pathology
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.