| Botrytis blight, also know as gray mold, is a fungal
disease caused by several species in the genus
Botrytis. It affects the buds, flowers, leaves, and
bulbs of many plants including: African violet,
begonia, chrysanthemum, cyclamen, dahlia,
geranium, lily, peony, rose, and tulip. The extent and
severity depends on weather conditions and cultural
practices. This disease is the primary cause of decay
in cut flowers.
Symptoms and Diagnosis
Botrytis blight causes buds and flowers to develop
abnormally and turn brown. Flowers may have
irregular flecks and brown spots; older flowers tend
to rot quickly. Soft, brown spots appear on leaves,
stem, and flowers following a cool damp period.
Affected parts may be covered with a gray mold
following damp, cool weather.
Life Cycle
Botrytis fungi overwinter as sclerotia on dead plant
debris in the garden. In the spring, spores form and
spread by wind or splashing water to infect dying,
wounded, or extremely soft plant tissues. Fungal
mycelial strands (web blight) from previously
infected plant parts can grow onto healthy plant
parts and infect them. The fungus is capable of
invading tissue during all periods of the growing
season and multiplies rapidly in declining foliage,
hence, the need for good sanitation.
Integrated Pest Management Strategies
1. Practice good sanitation. Remove and destroy all
infected plant parts as soon as they are observed.
2. Avoid overcrowding. Give adequate space
between plants to allow for good air circulation.
The fungus thrives in areas that are cool and
moist and where plants are overcrowded.
3. Do not overfeed. Avoid fertilizing with excessive
amounts of nitrogen. This can cause tender
growth that is very susceptible to the fungus. Get
a soil test to guide fertilizer practices.
4. Avoid overhead watering. Water on foliage and
flowers from overhead irrigation, especially on
cool, cloudy days, promotes the disease. Try to
keep buds and flowers dry. Water early in the day
so the plants have enough time to dry off
completely.
5. Use fungicides. Depending upon the
susceptibility of the plant to this disease, spray
every 10 days with a fungicide. Pesticides
registered for use include copper, captan,
chlorothalonil (Daconil), mancozeb, maneb,
sulfur, and thiophanate methyl (Cleary 3336).
Fungicides must be applied in advance of the
disease as a protectant. |
