| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Anthracnose |
Definite yellow spots
form on leaves and stems. These turn white and have a brown
border. Leaves die as do entire plants if stems are girdled. |
Colletotrichum antirrhini |
Heat and ventilate to maintain low humidity.
Water in a manner that keeps foliage surfaces dry. Apply azoxystrobin,
mancozeb, or ziram to protect healthy plants. |
| Botrytis Blight |
Petals turn brown and are covered with gray,
fungal growth. |
Botrytis cinerea |
Space plants to insure good air circulation.
Maintain low humidity. Avoid watering late in the day. Remove
crop debris. Apply chlorothalonil, fludioxonil, iprodione, or
mancozeb. |
| Downy Mildew |
Seedlings and cuttings are stunted and leaves
curl downward. Gray to white fungus lightly covers the underside
of leaves. Upper side of infected leaves have yellowed areas.
The fungus causes a systemic infection of all leaves of seedlings.
Older plants yellow, may be stunted, and die from the top down.
Plants fail to flower. |
Peronospora antirrhini |
Heat and vent to maintain low humidity, especially
when weather is cool and cloudy. Water in a manner that keeps
leaf surfaces dry. Spray azoxystrobin to cover all leaf surfaces.
Before replanting greenhouse beds, steam the soil because the
fungus survives in debris. |
| Phyllosticta Blight or Leafspot |
Yellow spots on leaves collapse and become black.
As these age, they become yellow or tan concentric rings. Small
black fungal fruiting structures for within the spots. |
Phyllosticta antirrhini |
Keep humidity low. Avoid wetting the plants when
watering. Remove and destroy crop debris. Apply a mancozeb fungicide. |
| Powdery Mildew |
White fungal growth forms on either surface of
lower leaves, also on stems of some cultivars. |
Oidium |
Heat and ventilate especially in the spring and
fall to reduce night humidity. Apply Ampelomyces,
triforine, triadimefon, myclobutanil, or thiophanate methyl
+ mancozeb. |
| Pythium Root Rot |
Root tips turn brown and die. Plants are yellowed,
stunted, wilt, and die. Older plants may survive if not placed
under moisture stress. |
Pythium spp. |
Plant in pasteurized raised beds. Do not recontaminate
beds. Apply metalaxyl, mefenoxam, propamocarb, etridiazole,
or etridiazole + thiophanate methyl to protect healthy plants. |
| Rhizoctonia Stem Rot |
Stems of seedlings or recent transplants collapse
at the soil line. A red-brown lesion forms at the base of the
stem. Older plants wilt and die with lesions at the base as
noted above. |
Rhizoctonia solani |
Plant in pasteurized raised beds. Apply fludioxonil,
flutolanil, PCNB, or iprodione as a soil drench to protect healthy
plants. |
| Rust |
Small yellow swellings form on leaves or stems
and burst to release rusty colored spores. Concentric
rings of spores form around the initial spot. |
Puccinia antirrhini |
Apply chlorothalonil, myclobutanil, mancozeb
+ thiophanate methyl, triadimefon, mancozeb, or triforine to
protect healthy plants. |
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