Viola Diseases
| Diseases | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Aster yellows | Leaves are yellowed and narrow rather than oval. An abnormally high number of shoots form. | Phytoplasma | Remove infected plants. Control leafhoppers. |
| Bacterial infection | An abnormally high number of shoots form. | Rhodococcus fascians | Remove infected plants. |
| Black root rot | Plants are yellowed, stunted and die. | Thielaviopsis basicola | Try to maintain the soil pH below 6.2 where the violets are growing. Provide good soil drainage. Apply iprodione + thiophanate methyl or fludioxonil. |
| Crown rot | Dying plants have white fungal growth on stems at the soil line. Small, golden-tan, mustard-seed sized structures dot the white growth. | Sclerotium rolfsii | Remove infected plants. Keep mulch away from the base of the plants. |
| Downy mildew | Leaves have purplish or yellowed areas. | Peronospora or Bremiella | Apply chlorothalonil, mancozeb, mancozeb + zinc, copper sulfate or copper hydroxide in the spring when cool, wet weather prevails. |
| Fungal leaf spots | Small spots, on generally on lower leaves, enlarge and become dark purple to black, 1/4” or more in diameter with feathery margins. Leaves then yellow. | Cercospora, Alternaria, Ascochyta, Botrytis, Centrospora, Ciborinia, Colletotrichum, Cryptostictis, Cylindrosporium, Heterosporium, Marssonina, Phyllosticta, Ramularia, Septoria | When irrigating, keep water off the foliage. Apply fludioxonil, chlorothalonil, mancozeb, mancozeb + zinc, copper sulfate, copper hydroxide, iprodione + thiophanate methyl, iprodione, chlorothalonil + thiophanate methyl, or potassium bicarbonate to protect leaves not yet infected. |
| Powdery mildew | White fungal growth develops on the upper surface of leaves. | Sphaerotheca | Apply mancozeb, mancozeb + zinc, myclobutanil, copper sulfate, copper hydroxide, sulfur, or potassium bicarbonate as soon as any white fungal growth is observed. |
| Pythium root rot | Plants wilt and die as lower stems and roots discolor and die. | Pythium | Remove infected plants. Apply mefenoxam or metalaxyl to protect healthy plants. |
| Rhizoctonia stem rot | Roots and stems brown as plants wilt and die. | Rhizoctonia | Remove infected plants. iprodione, iprodione + thiophanate methyl, or fludioxonil to protect healthy plants. |
| Rust | Pustules yellow-orange spores form on the underside of leaves. The upper side of the spot is yellow. | Puccinia or Uromyces | Avoid overhead irrigation. Apply myclobutanil or chlorothalonil. |
| Scab | White spots with purple edges form slightly swollen areas along petioles and leaf veins. | Sphaceloma violae | Apply thiophanate methyl, chlorthalonil, mancozeb, or chlorthalonil + thiophanate methyl to protect leaves not yet infected. |
Active Ingredients and Trade Names of the Chemicals
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic chemicals, are said to be ‘at risk’ to the development of resistance if they are used repeatedly. See the Risk Level in the table; 1 = low risk; 2 = moderate risk; 3 = high risk. Fungicide Resistance Action Committees (FRAC) have developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action. That is, chemicals with the same FRAC number kill the fungus in the same way (See http://www.frac.info/frac/index.htm). If a fungus has resistance to a chemical with a particular FRAC number, it is most likely resistant to all the other chemicals with that same number. 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).
| FRAC Group | Risk | 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) Dovetail (81943-14) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138) Chipco 26019 (264-481) OHP 26 (432-888-59807) Raven (81943-13) |
| 3 | 2 | Triazole | triadimefon | 12 | Strike (3125-436) |
| myclobutanil | 24 | Eagle (62719-463) Systhane (707-253) | |||
| 4 | 3 | Acylanine | mefenoxam | 0 | Fenox (70252-11-48234) |
| metalaxyl | 12 | Vireo MEC (81943-28) | |||
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| M | 1 | Chloronitrile | chlorothalonil | 12 | Chlorosel (72167-25-72159) Fungonil (60063-9-4) Pegasus (72167-24-1812) Equus (72167-27-66222) |
| Copper, complex | copper sulfate | 12 24 | Camelot (1812-381) Phyton 27 (49538-3) | ||
| Copper fixed | copper hydroxide | 48 | CuPRO (67690-37) | ||
| Dithio-carbamate | mancozeb | 24 | Dithane (707-180) FORE (707-87) Pentathlon ((1818-251) Protect DF (1001-77) | ||
| manganese + zinc | 24 | Wingman (81943-22) | |||
| M | 1 | Copper, complex | copper sulfate | 12 24 | Camelot (1812-381) Phyton 27 (49538-3) |
| Copper fixed | copper hydroxide | 48 | CuPRO (67690-37) | ||
| NC | 1 | potassium bicarbonate | 4 | Armicarb (5905-541-AA) Milstop (70870-1-68539) | |
| sulfur | 24 | Kumulus (51036-352) | |||
| Combined products | |||||
| 12 + 1 | 3 | iprodione + thiophanate methyl | 12 | 26/26 Fungicide (432-1414-1001) | |
| 1 + M | 1 | thiophanate methyl + chlorothalonil | Spectro 90 (1001-72) |
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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