| Disease (causal
agent) |
Symptoms |
Survival of pathogen and effect
of environment |
Comments on control |
Bacterial canker
(Curtobacterium flaccumfaciens pv. poinsettiae) |
Longitudinal water-soaked lesions on stems and petioles.
Spotting of leaves and defoliation. In advanced stages, stem lesions
split open. |
Infected poinsettia plants and debris. Favored by warm,
moist conditions. Bacteria spread in water. Bacteria may be present
in symptomless plants and cuttings. |
Plant pathogen-free cuttings. Avoid overhead irrigation
and syringing. Steam soil and disinfect benches with copper naphthenate;
disinfect tools. |
Bacterial stem rot
(Erwinia chrysanthemi) |
Watery, soft rot of cuttings or stems, resulting in
disintegration of infected tissues. Rot develops rapidly and plant
collapses. |
In diseased plant tissues. Favored by high temperatures
(73° to 86°F) and succulent plants. |
Avoid high temperatures and practices that produce succulent
growth. Careful sanitation practices will minimize spread of bacteria.
Disinfect tools with quaternary ammonium. |
Gray mold
(Botrytis cinerea) |
Blasting of flowers and browning or spotting of bracts.
Woolly gray fungal growth forms on dead parts. Lesions on stems and
leaves. |
In plant debris. Favored by cold, moist conditions and
condensed moisture on bracts and flowers. |
Provide better growing conditions and air circulation.
Clean up plant debris. Avoid wetting leaves and try to lower relative
humidity. Protect plants with fenhexamid. more
info |
Greasy canker
(Pseudomonas viridiflava) |
Greasy-appearing cankers on stems. Necrotic lesions
with chlorotic margins on leaves. Sometimes confused with bacterial
canker. |
Infected plant debris. Bacterium has a wide host range.
Disease favored by high humidities, high temperatures, and condensed
moisture on plants. |
Reduce humidity. Sanitize pruning tools. Avoid wetting
foliage. |
Powdery mildew
(Eurphorbia pulcherrima) |
Yellow spots or whitish growth on upper leaf surfaces
and bracts. |
On living plants. Favored by moderate temperatures and
crowded, shaded foliage. |
Regularly inspect plants. Remove, bag, and dispose of
infected plants at first sign of infection. Apply protectant fungicide
when plants are young and more easily sprayed. more
info |
Root and stem rot
(Thielaviopsis basicola, Rhizoctonia solani, Pythium spp.) |
Plants are stunted and wilt easily. Lower leaves become
chlorotic and may fall. Roots are rotted and dark brown, water-soaked
stem lesions develop. Large roots and lower stem may be enlarged and
ridged. Young plants frequently are killed. Each fungus can produce
disease independently, or fungi may interact to produce rapid decline.
Symptoms vary with the pathogen. |
In soil. Favored by excess moisture and overcrowding
of plants. Thielaviopsis and Pythium severe at high
(86°F) or low (63°F) soil temperatures, whereas Rhizoctonia
develops most rapidly between 63° to 79°F. Disease development
most severe at rooting and just before maturing. |
Plant disease-free cuttings in heat-treated or chemically
treated soil. Before planting, mix into soil mefenoxam plus thiophanate-methyl.
If root rots occur after potting, drench with mefenoxam plus thiophanate-methyl.
more info |
Rust
(Uromyces euphorbiae) |
Pustules of cinnamon-brown
spores on both leaf surfaces. |
On living plants. Favored by moist conditions. |
Pick off and burn diseased leaves. Protective fungicide
sprays help in control. more info |
| Spot anthracnose or scab (Sphaceloma poinsettiae) |
Circular, buff-colored spots that develop into scablike
lesions on leaves and stems. |
Infected plants and debris. Favored by wet conditions.
Spores spread in water. |
Do not wet foliage. Protective fungicidal sprays should
help in control. Avoid splashing water. |
| |
| Virus or viruslike disease |
Symptoms |
Host range and natural spread |
Comments on control |
Mosaic
(Poinsettia mosaic virus) |
Distortion of leaves and bracts. Some bracts may fail
to color normally. Mild mottling of leaves. Angular leaf spotting,
apparent only under cool temperatures. Symptoms most severe on plants
grown at 61° to 68°F. Plants grown at 75° to 82°F
appear normal. |
May be symptomless in poinsettias. Mechanically transmitted. |
Obtain virus-free plants. Grow at higher temperatures.
Discard plants with symptoms. |
Poinsettias are also susceptible to Rhizopus soft rot (Rhizopus
stolonifera).
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
R. D. Raabe (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego Co.
A. H. McCain (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
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