Marigold Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| ALTERNARIA LEAF SPOT | Purplish spots form on leaves and stems. | Alternaria | Avoid overhead irrigation. Apply chlorothalonil, propiconazole, iprodione, fludioxonil, azoxystrobin, neem oil, myclobutanil, copper hydroxide, mancozeb, or thiophanate methyl + mancozeb. |
| BACTERIAL LEAF SPOT | Small (2-5 mm) circular dead spots form on leaves and petioles. Spots have purple margins. | Pseudomonas tagetis | Destroy infected plants. Avoid overhead irrigation. |
| BOTRYTIS FLOWER BLIGHT | Flower parts brown and die. Gray masses of spores form on the infected tissue when wet. | Botrytis cinerea | Avoid overhead irrigation. Apply chlorothalonil , fludioxonil, azoxystrobin, iprodione, mancozeb, thiophanate methyl + mancozeb, or ferbam. |
| FUSARIUM WILT | Seedlings are killed. In older plants, black streaks darken the vascular tissue up one side of the plant. Plants wilt. Roots on the greatly reduced root system are rotted. During wet weather, salmon-colored spore masses form on infected stems. | Fusarium oxysporum | Plant in potting mix free of pathogens. Destroy infected plants. |
| LEAF BURN | The tips and margins of leaves yellow and die. | Excess boron, manganese, or molybdenum | Measure and apply micronutrient solutions carefully. Manganese should not be above 55 ppm, molybdenum above 24 ppm, or boron above 3 ppm. |
| SEPTORIA LEAF SPOT | Oval to irregular gray to black spots with tiny dots peppering their surface (fungal fruiting structures) form first on lower leaves and then spread upward. | Septoria tageticola | Avoid overhead irrigation. Apply propiconazole, fludioxonil or chlorothalonil. |
Alternaria leaf and stem spot.
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.) |
|---|---|---|---|---|---|
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| 3 | 2 | Triazole | propiconazole | 24 | Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943) |
| myclobutanil | 24 | Systhane (707-253) | |||
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| M | 1 | 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) | ||||
| Copper, fixed | copper hydroxide | 48 | Kocide (352-656), Champion (55146-1) | ||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) | |||
| ferbam | 24 | Ferbam (45728-7) | |||
| NC | 1 | neem oil | 4 | Trilogy (70051-2), Triact (70051-2-59807) | |
| Combined | 1 |
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).
DISCLAIMER
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.
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