| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Bacterial Blight |
Dark, reddish-brown to black rotting areas form
on roots and crown. Infected petioles have a greasy appearance. |
Erwinia chrysanthemi |
Pot and propagate in pasteurized media. Do not
take cuttings from infected plants. Avoid high-temperature,
high-humidity conditions. Keep plants separate from new plants,
especially foliage plants of unknown health. |
| Botrytis Blight |
Small water-soaked lesions form on damaged petioles
and spread to leaf blades. Infected flowers fade prematurely. |
Botrytis cinerea |
Space plants and provide ventilation to avoid
excessively high humidity. Remove fading flowers and yellowing
leaves. Apply chlorothalonil, fenhexamid, copper sulfate, or
mancozeb to protect healthy tissue. |
| Foliar Nematode |
Small tan, sunken areas form on lower surfaces
of leaves. Spots become dry and dull black as they enlarge.
Plants are stunted. |
Aphelenchoides ritzema-bosi |
Destroy infected plants. Water plants in a manner
that keeps leaf surfaces dry and does not splash from plant
to plant. |
| Phytophthora Crown Rot |
Crowns and roots have a dark, water-soaked appearance.
This spreads to the petioles
and leaf blades. Leaves remain firmly attached as the plant
collapses. |
Phytophthora nicotianae
var. parasitica; P. nicotianae var. nicotianae; P. cryptogea |
Do not propagate from infected plants. Pot in
pasteurized media Destroy infected plants. Apply etridiazole,
etridiazole + thiophanate methyl, propamocarb, mefenoxam, or
metalaxyl to protect healthy plants. |
| Powdery Mildew |
White, mealy fungal growth on the leaves and
flowers causes them to dry and die. |
Oidium |
Syringe plants when the humidity is low in order
to inhibit mildew spore germination. Apply Ampelomyces,
myclobutanil, triadimefon, piperalin, or copper sulfate. |
| Pythium Root Rot |
Roots are dark brown. Plants are wilted and yellowed. |
Pythium spp. |
Do not overwater plants. Pot in pasteurized media.
Keep hose ends off the ground. To protect healthy plants, apply
etridiazole, etridiazole + thiophanate methyl, metalaxyl, mefenoxam,
or propamocarb to protect plants. |
| Rhizoctonia Crown Rot |
Plants wilt, collapse, blacken, and die. A reddening
of infected tissue may occur at soil line. Leaves readily detach
from collapsing plants. |
Rhizoctonia |
Destroy infected plants. Pot in pasteurized media.
To protect healthy plants, apply fludioxonil, PCNB, or etridiazole
+ thiophanate methyl. |
| Ring Spot |
Bright yellow or bleached ring patterns form
on dark green leaves. |
Irrigation water much colder or warmer than the
leaf surface causes cells to collapse. |
Keep irrigation water off the foliage. Use water
that is at room temperature |
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