| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Ascochyta Ray Blight |
Flower development is retarded on
one side of the bud. Petals exhibit a brown discoloration. Browning
and blackening extends down the stem, causing the flower to
droop. Brown to
black irregularly shaped spots develop on leaves. |
Ascochyta
(Mycosphaerella) |
Avoid overhead irrigation. Apply
chlorothalonil, mancozeb, iprodione, or thiophanate methyl +
mancozeb as a foliar spray. |
| Alternaria or Stemphylium Speck |
Pinpoint dead spots develop on petals.
These spots may not enlarge. If enough spots are present, the
entire flower dies. |
Alternaria
or Stemphylium |
Avoid overhead irrigation. Maintain
greenhouse humidity below 98%. Apply chlorothalonil, fludioxonil,
copper hydroxide, or mancozeb as a foliar spray. |
| Bacterial Blight |
Cuttings turn dark brown and collapse.
Surviving cuttings may be infected but have no symptoms. Established
plants wilt during the day when infected and recover at
night. |
Erwinia
chrysanthemi |
Purchase culture-indexed cuttings
that are free of the pathogen. Disinfect propagation beds between
crops. Destroy infected cuttings. |
| Bacterial Leaf Spot |
Small dark brown to black spots on
lower leaves enlarge and become irregular in shape. When infected
leaves dry, the spots
become brittle and crack. The disease often spreads up plants
in one side of the pot, eventually
to the flowers. |
Pseudomonas
cichorii |
Do not plant infected cuttings. Avoid
overhead irrigation. Water in a manner that keeps leaf surfaces
dry at all times. Protect plants grown outdoors from splashing. |
| Botrytis Blight |
Light brown spots form on lower petals.
Browning spreads
to other petals. Infected tissues become covered with dusty
gray spores. |
Botrytis
cinerea |
Maintain greenhouse humidity below
98% at all times. Apply chlorothalonil, copper, fludioxonil,
iprodione, or mancozeb as a foliar spray. |
| Chlorotic Mottle |
Leaves, at first mottled, become
completely yellow. Infected plants grown under low light conditions
and when temperatures average less than 20°C (69°F)
exhibit no symptoms. |
Chrysanthemum chlorotic mottle viroid |
Purchase virus-indexed plants that
are free of the pathogen. Destroy infected plants and disinfest
tools used to handle them. Do not handle healthy chrysanthemums
after handling infected plants. |
| Foliar Nematode |
V-shaped
yellow areas develop between the veins. These become water soaked,
then brown and dry. Some cultivars are symptomless however. |
Aphelenchoides
ritzema-bosi or A. fragariae |
Purchase indexed cuttings free of
the pathogen. Plant in pasteurized soil or soilless mix. Water
in a manner that keeps plant surfaces dry. Remove and destroy
infected plants and debris. |
| Fusarium Wilt |
Symptoms vary with the cultivar infected.
Yellowing of leaves, wilting, and discoloration of the vascular
tissue develops up one side of the plant. |
Fusarium
oxysporum |
Management: Purchase culture-indexed
cuttings free of the pathogen. Plant in pasteurized soil or
soilless mix free of the pathogen. Maintain soil pH between
6.5 and 7.0. Use nitrate rather than ammonium forms of fertilizer.
Apply thiophanate methyl. |
| Powdery Mildew |
Leaves have white, dry fungal growth
on their surfaces. |
Erysiphe
cichoracearum |
Apply Ampelomyces,
fenarimol, myclobutanil, piperalin, or triadimefon. |
| Pythium Root and Stem Rot |
Stems turn dark brown to black at
the soil line. Plants are stunted, wilt, and die. Outer
parts of the root brown and strip off. |
Pythium |
Plant in pasteurized soil or soilless
mix free of the pathogen. Apply etridiazole, metalaxyl, propamocarb,
mefenoxam, or thiophanate methyl + etridiazole as a soil drench. |
| Rhizoctonia Stem Rot |
Young infected plants wilt during
the day and recover at night. Reddish-brown dead areas develop
at the soil line and girdle the plant. |
Rhizoctonia
solani |
Plant in pasteurized soil or a soilless
mix free of the pathogen. Apply flutolanil, PCNB or thiophanate
methyl + etridiazole as a soil drench. |
| Stunt |
Symptoms vary with the cultivar infected.
Young leaves are light green and very upright. Plants are stunted
to half their normal height at maturity. Infected plants flower
prematurely and flower size is reduced. Some cultivars exhibit
small dead spots or flecks on the leaves. |
Chrysanthemum stunt viroid |
Purchase virus-indexed plants that
are free of the pathogen. Destroy infected plants and disinfest
tools used to handle them. Do not handle healthy chrysanthemums
after handling infected plants. |
| Verticillium Wilt |
The margins of lower leaves wilt
and die. Or, the entire leaf dies. Symptoms proceed up one side
of the plant. |
Verticillium |
Plant in pasteurized soil or soilless
mix free of the pathogen. |
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