Snapdragon (Antirrhinum) Diseases
Gary W. Moorman, Professor of Plant Pathology
| 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 mancozeb, ziram, or azoxystrobin 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 chlorothalonil, iprodione, mancozeb, captan, or fludioxonil. | |
| 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. Spray azoxystrobin, potassium salts of phosphorus acid or trifloxystrobin to cover all leaf surfaces. 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 myclobutanil, propiconazole, thiophanate methyl, triforine, triadimefon, or thiophanate methyl + mancozeb. | |
| 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 mefenoxam, dimethomorph, potassium salts of phosphorus acid, etridiazole, or etridiazole + thiophanate methyl 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 PCNB, flutolanil, or iprodione as a soil drench 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 chlorothalonil, mancozeb + thiophanate methyl, triadimefon, mancozeb, maneb + zinc, or triforine to protect healthy plants. |
Anthracnose.
Downy mildew.
Rust.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade Names (EPA Reg. no.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| 3 | 2 | Imidazole | triflumizole | 12 | Terraguard (400-433) |
| Piperazine | triforine | 12 | Triforine (241-355) | ||
| Triazole | propiconazole | 24 | Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943) | ||
| triadimefon | 12 | Strike (3125-436), Bayleton (432-1360) | |||
| myclobutanil | 24 | Systhane (707-253) | |||
| 4 | 3 | Acylanine | mefenoxam | 0 | Subdue MAXX (100-796) |
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| trifloxystrobin | 12 | Compass (432-1371) | |||
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| 14 | 1 | Aromatic | |||
| hydrocarbon | PCNB | 12 | Revere (400-407-10404), Blocker (5481-211), Terraclor (400-399), Defend (5481-444-1001) | ||
| Thiadiazole | etridiazole | 12 | Truban (58185-7), Terrazole (400-416) | ||
| 40 | Cinnamic acid | ||||
| derivative | dimethomorph | 12 | Stature (241-419-67690) | ||
| M | 1 | Phthalimide | captan | 96 | Captan (66330-29) |
| Chloronitrile | chlorothalonil | 48 | Daconil (50534-9), Exotherm Termil (70-223) | ||
| 12 | Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812) | ||||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) | |||
| ziram | 48 | Ziram (4581-140) | |||
| U | 1 | Phosphonate | fosetyl-Al | 12 | Aliette (432-890) |
| Phosphite | phosphorus acid salts | 4 | Alude (71962-1-1001) | ||
| potassium phosphate | 4 | Vital (42519-24) | |||
| Combined products | 1 | ||||
| 1 + M | thiophanate methyl + etridiazole | Banrot (58185-10) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
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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.
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