Dahlia Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| ASTER YELLOWS | Leaf-like tissue forms where flower parts should be located. Flower-like parts remain green or light green. | Phytoplasma | Destroy infected plants. Control leafhoppers. |
| BACTERIAL STEM ROT | Blackened stems have a soft, wet, interior and a foul odor. | Erwinia carotovora | Promptly destroy infected plants |
| GRAY MOLD | In wet weather, masses of gray spores form on brown spots on buds, leaves or stems. | Botrytis cinerea | Maintain low relative humidity. Apply fludioxonil, iprodione or mancozeb to protect plants. |
| POWDERY MILDEW | Dry, white, mealy, fungal growth occurs on the upper surface of leaves. | Golovinomyces cichoracearum (formerly Erysiphe) | Apply mancozeb, thiophanate methyl + mancozeb, fenarimol, piperalin, sulfur, triadimefon, myclobutanil, ziram, or triforine when the fungus is first observed. |
| STORAGE ROT | Tubers decay into a soft smelly mass. | Various fungi and bacteria. | Avoid wounding the tubers. Let the tuber surfaces dry and remove soil before storing. Store tubers in a cool, dry location. |
| VERTICILLIUM WILT | Single branches or the entire plant wilts and dies. Vascular tissue in affectes stems is black, dark brown, or greenish-brown. | Verticillium | Plant in pathogen-free potting mix. |
| VIRUS | Conspicuous rings and line patterns may be present or a mosaic of light and dark green may occur on leaves. | Impatiens necrotic spot virus | Discard infected plants. Do not save tubers from affected plants. Control thrips since they vector the virus. |
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 | Imidazole | fenarimol | 12 | Rubigan (62719-134) |
| Piperazine | triforine | 12 | Triforine (241-355) | ||
| Triazole | triadimefon | 12 | Strike (3125-436), Bayleton (432-1360) | ||
| myclobutanil | 24 | Systhane (707-253) | |||
| 5 | Piperidine | piperalin | 24 | Pipron (67690-1) | |
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| M | 1 | Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) |
| manganese + zinxc | 24 | Protect T/O (1001-65) | |||
| NC | 1 | sulfur | 24 | Kumulus (51036-352) | |
| Combined products | 1 | ||||
| 1 + M | thiophanate methyl + mancozeb | Zyban (58185-31) |
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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