| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Alternaria leaf spot* (Alternaria tenuis) |
Water-soaked areas occur on undersides of leaves. Spots enlarge to 0.25 to 0.5 inch and have a slightly sunken center surrounded by concentric rings of darker brown or red tissue. Common on Pelargonium domesticum. | In plant debris and leaf spots. Favored by cool wet conditions. | Protect foliage with mancozeb. Iprodione sprays applied for gray mold also may help. |
| Bacterial blight * (Xanthomonas axonopodis pv. pelargonii) |
Round sunken leaf spots or angular dead areas appear and are followed by wilting and death of leaf. Systemic infection results in defoliation and frequently death of plant. Infected stems are blackened and shriveled. Black streaks may occur in nonrotted portions of stem. Older plants may not exhibit symptoms. | In infected cuttings and plants and in plant debris in soil for 1 year. Disease develops rapidly at high temperatures. Bacteria are spread in water and can be vectored by greenhouse whitefly from diseased to healthy geranium plants. | Use disease-free propagative material and observe strict sanitation. Steam or chemically treat rooting media. Disinfect cutting knives in a solution containing quaternary ammonia. Avoid overhead irrigation. |
| Bacterial leaf spot (Pseudomonas cichorii) |
Dark brown to black, irregularly shaped spots (0.25 to 1 inch in diameter). Margins are water-soaked. Spots may develop tan centers and have a yellow halo. | Infected plants. Many kinds of plants are susceptible. Favored by warm temperatures, rain, and overhead irrigation. | Avoid overhead irrigation. Maintain sanitation. |
| Blackleg and root rot * (Pythium spp.) |
Brown water-soaked bases of cuttings and young plants. Lesions enlarge rapidly, move up the stem, and turn black. Affected plants wilt and die. | Soilborne. Favored by overwatering and poor drainage. | Follow recommendations above. Drench plants with oomycete (water mold) specific fungicide. Remove and destroy infected plants. |
| Edema (nonparasitic) |
Small, water-soaked, pimplelike spots appear on undersides of leaves and stems. Spots later become corky. | Favored by cloudy, cool weather. Actual cause unknown. | Do not overwater. Keep humidity low. Maintain higher temperatures. |
| Gray mold * (Botrytis cinerea) |
Brown water-soaked decay of flowers occurs. Fuzzy gray fungal spores form on rotted tissues. When infected flower parts fall on leaves, they also rot. Disease may affect stems. | In plant debris, especially flowers. Favored by cool wet conditions and water on plant. | Protect plants with chlorothalonil, iprodione, or fenhexamid. Where practical, remove old blossoms and dead parts. Avoid overhead irrigation. |
| Rust * (Puccinia pelargonii-zonalis) |
Pustules of orange-brown spores form on undersides of leaves. | On living leaves. Favored by moist conditions and water on plants. Spores are airborne. | Protect foliage with triadimefon and myclobutanil. Lower humidity to avoid condensation of water on leaves. Mancozeb also will help control rust. |
| Verticillium wilt * (Verticillium dahliae) |
Lower and middle leaves wilt, yellow, die, and fall. Shoots die back. Plants are stunted. In later stages, water-conducting tissues (xylem) may be discolored. | Remains in soil for many years. Also spread by infected cuttings and plants. Fungus has wide host range (tomato, strawberry, chrysanthemum, nightshade, and many others). Favored by moderate temperatures. Symptoms most severe in warm weather. | Use pathogen-free cuttings. Steam treat or fumigate soil with chloropicrin or a chloropicrin combination. Avoid soil previously planted to tomatoes, strawberries, potatoes, chrysanthemums, or other susceptible crops. |
| Virus or viruslike disease | Symptoms | Host range and natural spread | Comments on control |
| Flower break (Pelargonium flower break virus) Leaf curl (Pelargonium leaf curl virus) Line pattern (Pelargonium line pattern virus) Mosaic (Cucumber mosaic virus) Ringspot (Tomato ringspot virus or Tobacco ringspot virus or both) |
Symptoms vary depending on viruses present, cultivar, and growing conditions. Symptoms include light and dark green mottling of foliage, chlorotic spotting, ring spotting, leaf distortions, leaf breaking, vein clearing, and others. | In infected geranium plants. Symptoms of some are masked during warm weather. | Obtain virus-free cuttings. Do not propagate from plants that have shown symptoms of virus. |
| Geraniums are also susceptible to Armillaria root rot * (Armillaria mellea), crown gall * (Agrobacterium tumefaciens), bacterial fasciation (Rhodococcus fascians), and cottony rot * (Sclerotinia sclerotiorum). | |||
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |