| 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 campestris pv. pelargoni) |
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 mefenoxam.
Remove and destroy infected plants. more
info |
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. Woolly 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. more info |
Rust
(Puccinia pelargoni-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. more info |
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 methyl bromide-chloropicrin combination. Avoid soil previously
planted to tomatoes, strawberries, potatoes, chrysanthemums, or other
susceptible crops. more info |
| |
| 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 and/or Tobacco ringspot virus)
Yellow net
(virus suspected) |
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. more
info |
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