Chrysanthemum Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| ASCOCHYTA RAY BLIGHT | Flower development is retarded on one side of the bud. Petals exhibit a brown discoloration. Browning and blackening extends down the stem, causing the flower to droop. Brown to black irregularly shaped spots develop on leaves. | Ascochyta (Mycosphaerella) | Avoid overhead irrigation. Apply chlorothalonil, propiconazole, fludioxonil, copper hydroxide, iprodione, or thiophanate methyl + mancozeb as a foliar spray. |
| ALTERNARIA OR STEMPHYLIUM RAY SPECK | Pin-point dead spots develop on petals. These spots may not enlarge. If enough spots are present, the entire flower dies. | Alternaria or Stemphylium | Avoid overhead irrigation. Maintain greenhouse humidity below 98%. Apply chlorothalonil, propiconazole, or iprodione as a foliar spray. |
| BACTERIAL BLIGHT | Cuttings turn dark brown and collapse. Surviving cuttings may be infected but have no symptoms. Established plants wilt during the day when infected and recover at night. | Erwinia chrysanthemi | Purchase culture-indexed cuttings that are free of the pathogen. Disinfect propagation beds between crops. Destroy infected cuttings. |
| BACTERIAL LEAF SPOT | Small dark brown to black spots on lower leaves enlarge and become irregular in shape. When infected leaves dry, the spots become brittle and crack. The disease often spreads up plants in one side of the pot, eventually to the flowers. | Pseudomonas cichorii | Do not plant infected cuttings. Avoid overhead irrigation. Water in a manner that keeps leaf surfaces dry at all times. Protect plants grown outdoors from splashing. |
| BOTRYTIS BLIGHT | Light brown spots form on lower petals. Browning spreads to other petals. Infected tissues become covered with dusty gray spores. | Botrytis cinerea | Maintain greenhouse humidity below 98% at all times. Apply chlorothalonil as a spray or fog or apply iprodione, mancozeb, trifloxystrobin, or fludioxonil as a foliar spray. |
| CHLOROTIC MOTTLE | Leaves, at first mottled, become completely yellow. Infected plants grown under low light conditions and when temperatures average less than 20° C (69° F) exhibit no symptoms. | Chrysanthemum chlorotic mottle viroid | Purchase virus-indexed plants that are free of the pathogen. Destroy infected plants and disinfest tools used to handle them. Do not handle healthy chrysanthemums after handling infected plants. |
| FUSARIUM WILT | Symptoms vary with the cultivar infected. Yellowing of leaves, wilting, and discoloration of the vascular tissue develops up one side of the plant. | Fusarium oxysporum | Management: Purchase culture-indexed cuttings free of the pathogen. Plant in pasteurized soil or soilless mix free of the pathogen. Maintain soil pH between 6.5 and 7.0. Use nitrate rather than ammonium forms of fertilizer. Apply thiophanate methyl as a soil drench. |
| POWDERY MILDEW | Leaves have white, dry fungal growth on their surfaces. | Golovinomyces cichoracearum (formerly Erysiphe) | Apply Ampelomyces, myclobutanil, piperalin, fenarimol, trifloxystrobin, propiconazole, or triadimefon. |
| PYTHIUM ROOT AND STEM ROT | Stems turn dark brown to black at the soil line. Plants are stunted, wilt, and die. | Pythium | Plant in pasteurized soil or soilless mix free of the pathogen. Apply potassium salts of phosphorus acid, etridiazole, mefenoxam, or thiophanate methyl + etridiazole as a soil drench. |
| RHIZOCTONIA STEM ROT | Young infected plants wilt during the day and recover at night. Reddish-brown dead areas develop at the soil line and girdle the plant. | Rhizoctonia solani | Plant in pasteurized soil or a soilless mix free of the pathogen. Apply flutolanil, PCNB, trifloxystrobin, iprodione, thiophanate methyl or thiophanate methyl + etridiazole as a soil drench. |
| STUNT | Symptoms vary with the cultivar infected. Young leaves are light green and very upright. Plants are stunted to half their normal height at maturity. Infected plants flower prematurely and flower size is reduced. Some cultivars exhibit small dead spots or flecks on the leaves. | Chrysanthemum stunt viroid | Purchase virus-indexed plants that are free of the pathogen. Destroy infected plants and disinfest tools used to handle them. Do not handle healthy chrysanthemums after handling infected plants. |
| VERTICILLIUM WILT | The margins of lower leaves wilt and die. Or, the entire leaf dies. Symptoms proceed up one side of the plant. | Verticillium | Plant in pasteurized soil or soilless mix free of the pathogen. |
Botrytis or gray mold.
Foliar nematode symptoms.
Ascochyta leaf symptoms.
Ascochyta stem symptoms.
Bacterial blight (Erwinia).
Bacterial leaf spot (Pseudomonas).
Pythium root rot.
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 | Pyrimidine | fenarimol | 12 | Rubigan (62719-134) |
| Triazole | propiconazole | 24 | Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943) | ||
| myclobutanil | 24 | Systhane (707-253) | |||
| 4 | 3 | Acylanine | mefenoxam | 0 | Subdue MAXX (100-796) |
| 5 | Piperidinie | piperalin | 24 | Pipron (67690-1) | |
| 11 | 3 | Strobilurin | 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) | ||
| 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) | ||||
| Combined product | 1 | ||||
| 1+M | thiophanate methyl + mancozeb | Zyban (58185-31) |
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.
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