| Gray mold or botrytis blight is caused by the fungus,
Botrytis paeoniae. It is the most common disease of
garden peonies. This destructive disease is very
prevalent during damp, rainy seasons.
Symptoms and Diagnosis
On peonies afflicted with botrytis, the young shoots
rot off at ground level when they are 5 to 8 inches
tall. The stems often have a water-soaked, cankerous
appearance. The leafy shoots wilt suddenly and fall
over. The rotted portion of the plant will become
covered with a soft brown or blackish mass of
spores. Just above the ground level, the stalk will be
covered with a gray mold which sheds large
numbers of spores. The spores are carried by wind
and insects to young leaves and flower buds and
cause a leaf blight and bud rot. Small buds that are
affected turn black and wither. Larger buds turn
brown and fail to open. During a severe outbreak of
the disease, 90% of the buds fail to develop. Open
flowers are affected occasionally, and they also turn
brown and later develop a covering of gray mold.
Life Cycle
Botrytis fungi are both saprophytic and parasitic. The
spore-producing structures of the fungus develop
along the base of the rotting stalks and survive in
debris left in the garden over the winter. In the
spring, spores form and spread to dying, wounded,
or extremely soft plant tissues. As the disease
progresses, a gray mold develops. The gray mold is
made up of spores that are either wind-blown or
splashed onto new tissues and infect.
Integrated Pest Management Strategies
1. Prevent infection. In early fall, cut down all old
leaves and stalks to ground level. This debris
should be destroyed and not composted. Apply
1 to 2 inches of mulch to bury debris.
2. Improve soil drainage. Plant peonies in welldrained
soil; heavy clay soils should be lightened
with organic material such as compost or peat
moss. They should not be planted so that water is
apt to cover their bases, nor should soil be
heaped about the leaf bases.
3. Move plants to a better location. Good air
circulation can reduce disease problems. Plant in
full sun or at least in part sun. Space plants
widely, at least 3 feet apart. Remove aging leaves
from plants.
4.Use disease-free roots. When planting new
plants, buy only from reputable dealers, or take
divisions only from healthy, disease-free plants.
5. Use a fungicide. Spray the plants with a fungicide
when young tips break through the ground.
Follow 2 weeks later with another application
and every 14 days thereafter until mid-June.
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.
6. Look for varieties that show some resistance to
the disease. | 
