| Disease (causal agent) |
Symptoms |
Survival of pathogen and effect of environment |
Comments on control |
Bacterial blight
(Erwinia chrysanthemi) |
Water-soaked lesions; pith becomes jellylike; tops turn
black and exude drops of liquid. Stem may break or split. |
In plant debris. Favored by high temperatures (80°
to 90°F), absence of free water, and high humidity. |
Use disease-free cuttings. Reduce humidity in growing
areas. Dip cuttings in streptomycin. |
Cottony rot
(Sclerotinia sclerotiorum) |
Stems rotted; flower rot is similar to gray mold. Cottony
fungal mass may occur on rotted tissues. Black sclerotia may form
inside or outside stems. |
Sclerotia in soil. Spores produced from sclerotia are
airborne but infect only through flowers and dead tissues. Favored
by high humidity. |
Same as for gray mold. Also, treat soil with PCNB before
planting and spray foliage with iprodione or thiophanate-methyl. more
info |
Crown gall
(Agrobacterium tumefaciens) |
Irregular or round galls on stems and sometimes leaves. |
Soil and galls. Infection favored by moist conditions. |
Destroy infected plants. |
Foliar nematode
(Aphelenchoides ritzema-bosi) |
Dark green, angular spots in leaves develop progressively
upward from base of plant. Leaves turn yellow. These nematodes are
rarely important in California. |
Adults can survive up to 3 years in dead leaves. Spread
by splashing water. Leaves need to be wet for infection to take place. |
Use disease-free plants. Discard infected plants. Avoid
overhead irrigation. Control weeds. Submerge infected plants in hot
water (115°F) for 10 minutes. |
Fusarium wilt
(Fusarium oxysporum
f. sp. chrysanthemi and f. sp. tracheiphilum) |
Unilateral chlorosis of one or more leaves near the
apex, followed by curvature of the stem towards the affected side.
As the disease progresses, there is a general chlorosis and wilt and
stunting of leaves. The vascular system becomes a reddish brown. |
Soilborne and carried in cuttings. Favored by high soil
temperatures (80°F). |
Use disease-free cuttings in clean soil. Treat soil
(see Verticillium wilt). Adjust pH of soil to 6.5 to 7.0 and use nitrate
nitrogen. Avoid planting highly susceptible cultivars ('Bravo', 'Cirbronze',
'Illini Trophy', 'Orange Bowl', 'Royal Trophy', 'Yellow Delaware').
more info |
Gray mold
(Botrytis cinerea) |
Brown, water-soaked spots on petals. Woolly gray fungal
spores form on decayed tissues. Rotting of lower leaves. Fungus may
enter and girdle stem. |
In plant debris. Favored by high humidity, low temperatures
(50° to 60°F), and water on plant. |
Keep humidity low; avoid overhead irrigation. Protect
foliage with a fungicide, especially lower dense foliage. Mist blooms
with chlorothalonil, iprodione, or fenhexamid. more
info |
Hollow stem
(Erwinia carotovora) |
Pith of rooting cuttings deteriorates and collapses.
Affected tissues are brown. Surviving plants do not grow satisfactorily
and pith collapse may extend upward involving several internodes.
'Red Torch', 'Tempo', and 'Tempter' are very susceptible. |
Bacteria may be present in vascular bundles of symptomless
chrysanthemums. Bacteria also present in undecomposed debris. Favored
by high temperatures and high moisture. |
Use disease-free cuttings. Reduce humidity in growing
areas. Streptomycin dips may be helpful. |
Powdery mildew
(Erysiphe cichoracearum) |
White powdery growth on leaves and stems. Found mainly
on older leaves. |
Airborne spores produced only on living plants. Favored
by high humidity, crowding of plants, and cool weather. |
Spray with piperalin to eradicate existing infections.
Protect foliage with myclobutanil, fenarimol, or triadimefon. more
info |
Pythium root rot and basal
stem rot
(Pythium spp.) |
Girdling black lesions occur near soil line. Plants
stunted as a result of reduced root system caused by root rot. Plants
may die. |
Soilborne fungus. Spores spread in water or in soil.
Favored by excess soil moisture and poor drainage. |
Treat soil as for Verticillium wilt. Drench plants with
mefenoxam. more info |
Ray blight
(Phoma chrysanthemi) |
Basal leaf and stem rot. Below ground stem infection
may cause a one-sided distortion and necrosis of foliage. Blackish
rot of petals (ray blight) may extend into flower stalk. |
In mum refuse. Waterborne spores. Favored by rainy weather. |
Use disease-free cuttings. Avoid wetting foli age and
keep humidity low. Protect foliage with chlorothalonil. |
Rhizoctonia stem rot
(Rhizoctonia solani) |
Stem rotted
at soil line. Plants stunted. Dark fungal strands may be visible with hand lens. May
kill plants. |
Soilborne fungus. Favored by warm, moist conditions. |
Avoid deep planting. Spray base of transplants with
thiophanate-methyl, chlorothalonil, or iprodione after planting, or
treat soil with PCNB before planting. |
Rust
(Puccinia tanaceti) |
Small pustules of powdery, chocolate-brown spores on
undersides of leaves and on stems. |
Airborne spores produced only on living plants. Free
moisture necessary for infection. Principally a field disease. |
Use resistant cultivars. Protect foliage with triadimefon
or mancozeb before rust starts to build up. Avoid wetting foliage.
Keep humidity low. |
Septoria leafspot
(Septoria obesa, S. chrysanthemi) |
Irregular or circular, brown or black dead spots develop
progressively upward from base of plant. Tiny black fungal fruiting
bodies in centers of spots. |
In plant debris and in soil debris for 2 years. Spores
spread in splashing water. Favored by wet weather. |
Protect foliage with a fungicide at first sign of disease.
Greenhouse: avoid wetting foliage. Keep humidity low. |
Verticillium wilt
(Verticillium dahliae) |
Yellowing and wilting of foliage, may be one-sided.
Leaves die and dry upward from the base of the plant. |
Soilborne for many years. Carried in cuttings and root
divisions. Favored by cool weather followed by hot weather during
flowering. |
Use resistant cultivars and pathogen-free plants. Fumigate
with chloropicrin-methyl bromide combination. In sunny climates, soil
solarization might be considered. more info |
White rust
(Puccinia horiana) |
Whitish pustules on the lower leaf surface. On the upper
surface the infection is evident as pale-green to yellow spots up
to an inch in diameter. Raised, waxy, pink-colored pustules are formed
on lower leaf surface. As they mature and produce spores, they turn
whitish in color. |
This microcyclic rust survives on living chrysanthemum
foliage. Teliospores in the leaf pustules germinate in place producing
basidiospores that are airborne and infect by direct penetration.
Favored by the same conditions as ordinary rust (cool, damp weather),
except that direct sunlight destroys airborne basidiospores. Principally
a greenhouse disease. |
Not all cultivars are susceptible. White rust is under
an eradication program in California. Check with your Agricultural
Commissioner about its status in your county. Once the disease is
confirmed, CDFA requires a control program of 3 to 5 applications
of myclobutanil (Eagle or Systhane); the number of applications depends
on whether or not the crop is in an infested or noninfested area
or if it is propagative material. Repeated treatments with myclobutanil
can cause stunting of growth, so don't apply it weekly throughout
the winter if white rust is not present and treatment not required
by law. Growers in nonregulated areas can rotate with mancozeb (Dithane)
and chlorothalonil (Daconil) as a protectant treatment program. Combine
fungicide treatments with destruction of infected plants and crop
free periods of 8 weeks. Propiconazole, previously recommended as
the treatment for eradication programs, may cause phytotoxic symptoms
on some cultivars. Infected plants or flowers cannot be moved or
sold and cleanup of infestations in quarantined areas must be done
to CDFA's satisfaction. |
| |
| Virus or viruslike disease |
Symptoms |
Host range and natural spread |
Comments on control |
Aspermy
(Tomato aspermy virus) |
Flower distortion and reduction in flower size. Color
break in florets of red, bronze, and pink cultivars. Foliar symptoms
not apparent. Some cultivars are symptomless. |
Transmitted by handling, cutting tools, and vegetative
propagation. Also transmitted by aphids. |
Use disease-free cuttings. Control aphids; remove infected
plants. |
Chlorotic mottle
(Chrysanthemum chlorotic mottle viroid) |
Mottling followed by complete chlorosis. May be confused
with nutritional problems. Symptoms somewhat masked under low light
and cool temperature conditions below 70°F. |
Spread by handling, cutting tools, and vegetative propagation. |
Use disease-free cuttings. Remove infected plants. |
Mosaic
(Chrysanthemum mosaic virus) |
Mosaic mottling of foliage. Dwarfing and deforming of
leaves, stems, and flowers. Symptoms variable, depending upon strain
of virus and cultivar. |
Transmitted by vegetative propagation and by aphids. |
Obtain disease-free plants. Control aphids. |
Spotted wilt
(Tomato spotted wilt virus, Impatiens necrotic spot virus) |
Frequently one-sided in plant. Ring patterns on leaves of some cultivars. Leaf
distortion and necrosis.
Dark necrotic streaks on stems. Flowers may be distorted and with
some necrosis. |
Thrips-transmitted; not spread by cutting knife, but
can be spread by vegetative propagation. Many weeds and perennial
ornamental plants act as reservoirs of virus (dahlia, calla, nasturtium,
mallow, knotweed, plantain, and others). |
Eliminate nearby susceptible ornamental plants and weeds.
Control thrips inside and outside growing areas. Use virus-free cuttings. |
Stunt
(Chrysanthemum stunt viroid) |
General stunting of plants. Foliage may be pale with
upright, young leaves. Flowers are smaller than normal and some cultivars
may flower 7 to 10 days early. |
Viroid is easily transmitted by handling, cutting knives,
vegetative propagation, etc. Not spread by aphids or thrips. Viroid
has a wide host range. Symptomless in some plants. |
Obtain disease-free plants from a propagation specialist
using an indexing program. |
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