Serious diseases of geranium, especially bacterial
blight, southern wilt, Pseudomonas leaf spot, and rust, can arrive
at your greenhouse on cuttings that are already infected. If you
do not keep geraniums all year and have a several-month period when
geraniums are not in your greenhouse, diseases on a new crop may
have come on infected cuttings. Therefore, inspect cuttings carefully
when they arrive for the symptoms described in this fact sheet.
Set aside any cuttings with symptoms and obtain a diagnosis of the
problem promptly. When plants have been in the greenhouse
for several days or weeks, it is not likely that a diagnostician
will conclude that the disease definitely came on the cuttings.
After planting is done, scout the crop frequently and thoroughly
early in the season for symptoms. This will help you find problems
and avoid serious disease losses later in the season. Encourage
all workers to watch for symptoms.
| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Alternaria Leaf Spot |
Water-soaked
spots on underside of leaf enlarge
to 1/4-1/2 inch. Concentric rings of dark tissue form
in spots. |
Alternaria tenuis |
Avoid overhead watering. Remove and destroy crop
debris from benches, pots, and walkways. Apply azoxystrobin,
copper hydroxide, chlorothalonil, fludioxonil, or mancozeb. |
| Bacterial Blight |
Two types of symptoms may develop: (1) Small
spots, less than 1/4 inch, develop on underside of the leaf
and become sunken and well defined. The leaf wilts and dies
as the bacterium spreads through water-conducting vessels of
vein and petiole. V-shaped
areas form with wide
part of V on leaf margins and point of V on veins; (2) Lower
leaves wilt
at margins while the blade and petiole
remain turgid. The vascular tissue of the main stem on the
side of the affected portion of the plant is discolored gray-brown
and may ooze bacteria
when cut. Lower leaves die and fall. |
Xanthomonas campestris
pv. pelargonii |
Purchase culture-indexed cuttings or grow plants
from seed. Immediately discard infected plants after a positive
diagnosis is made. Avoid overhead irrigation. Discard all unwanted
geraniums at season's end. Do not take cuttings with knives.
Wash hands frequently when breaking out cuttings. Or disinfest
the cutting knife by dipping in alcohol and flaming or leaving
in ZeroTol* or 1 Clorox* to 9 parts water for 10 minutes. |
| Bacterial Fasciation |
Short,
thick, fleshy, aborted stems that form at base of main stem
at or below soil level are pale green or green-yellow. The rest
of the plant appears healthy. |
Rhodococcus fascians |
Purchase culture-indexed plants. Discard infected
stock plants and cuttings and infested media. |
| Blackleg |
Cuttings first develop a brown water-soaked rot
at the base. The coal black rot proceeds 3-4 inches up stem
and kills the cutting rapidly. |
Pythium |
Use sterile propagation media. Discard infected
cuttings since affected rooted cuttings later develop root rot
(see Pythium Root Rot). Keep hose ends off the ground. |
| Botrytis Blight |
Flowers
turn dark and fall prematurely. Where infected petals land
on leaves, an irregular
leaf spot forms. Cutting stubs have a brown rot that may
extend down stem. Cuttings develop a dark
brown rot near the base. |
Botrytis
cinerea |
Avoid damaging plants in any way. Do not leave
large cutting stubs. Remove and destroy fading flowers and leaves.
Heat, ventilate, and space plants to ensure good air circulation
and low humidity. Apply a mixture of chlorothalonil & mancozeb.
Use copper hydroxide, fenhexamid, fludioxonil, or iprodione
alone only once as a final clean up of the crop and only if
disease pressure is low. |
| Edema |
Small water-soaked
pimples or blisters form on the underside of lower leaves.
Blisters become
corky brown. Severely affected leaves fall. |
This physiological disorder is favored by cool,
cloudy weather. |
Space plants to provide good air circulation.
Plant in well-drained mix. Avoid over watering during cool,
cloudy weather. |
| Leaf Burn |
Oldest leaves have yellow spots between the veins.
Yellowing increases between the veins as dead spots appear.
The margins of leaves die. |
Iron excess |
Symptoms can be confused with mite injury and
edema. Avoid using too much micro nutrient fertilizer. Maintain
soil pH above 5.5. Keep the ratio of iron and manganese close
to 1:1 in the fertilizer. Avoid over fertilization |
| Pseudomonas Leaf Spot |
Elliptical, water-soaked 1/4- to 1/2-inch spots
form on leaves. Spots become dark brown to black and irregularly
shaped. A yellow halo may or may not surround each spot. |
Pseudomonas cichorii |
Purchase disease-free cuttings. Do not irrigate
overhead. Keep leaf surfaces dry at all times. |
| Pythium Root Rot |
Root tips appear translucent and water-soaked
and contain microscopic
spores. The outer layers of root tissue strip
off when pulled from soil leaving the central core of vascular
tissue bare. The
fungus may invade the lower stem. |
Pythium |
Pot in sterile media. Keep hose ends off the
ground. Discard blackleg-infected cuttings even if well rooted.
Apply fosetyl-Al, mefenoxam, etridiazole, etridiazole + thiophanate
methyl, metalaxyl, or propamocarb. |
| Rust |
Chlorotic specks on upper leaf surface appear
directly opposite pustules of rust-colored spores on underside
of leaf. Spores erupt in concentric rings forming a "target"
spot. |
Puccinia pelargonii-zonalis |
Purchase rust-free cuttings. Do not irrigate
overhead. Discard unwanted geraniums at season's end. Apply
chlorothalonil, myclobutanil, flutolanil, oxycarboxin, or triadimefon
to protect plants. |
| Southern Bacterial Wilt |
Lower leaves wilt, yellow, and fall. Vascular
tissue of affected stems turns brown or black. |
Pseudomonas solanacearum |
Purchase culture-indexed plants. Do not bring
ground-planted geraniums into the production area or propagate
from them. Destroy infected plants. |
| Verticillium Wilt |
Middle and upper leaves collapse, dry, and fall.
Vascular tissue of affected stems is browned. Symptoms are readily
confused with those of bacterial blight. |
Verticillium albo-atrum
or V. dahliae |
Purchase culture-indexed cuttings. Use sterile
potting mix. Destroy infected plants. |
| Viruses |
Symptoms vary with virus, cultivar, and growing
conditions. Symptoms include: mottling, ring spotting, leaf
cupping, yellowing
of veins, leaf malformation, leaf spotting, and loss of
zonation. |
Many viruses occur singly and in various combinations
in plant tissue. |
Purchase virus-indexed cuttings. Maintain strict
insect and mite control. |
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