| Disease (causal agent) |
Symptoms |
Survival of pathogen and effect of environment |
Comments on control |
Gray
mold
(Botrytis cinerea or
B. paeoniae) |
Leafy shoots wilt and fall over as
a result of rotting at the base. Woolly gray fungus sporulation is usually
visible on infected tissues. Flower buds darken and wither; leaves also may be attacked. |
Disease is favored by wet weather
and injured tissue. Fungus survives on plant debris and as sclerotia in or on soil. |
Remove or burn old growth in fall.
Cut stalks below the ground level. Planting on raised beds also is helpful.
Treat with fenhexamid. more info * |
Leaf blotch
(Cladosporium paeoniae) |
Small (0.02 to 0.04 inch), oval
leaf spots that reach a diameter of 0.08 to 0.12 inch before they penetrate
through the thickness of leaf. As spots enlarge, they merge giving the leaf
an irregular, blotchy appearance. The upper surface of spots become purple while the lower surface is a dull brown. |
Fungus survives on infected peony
debris and probably on infected scales of crown buds. Disease is favored by rainy weather in spring. |
Burn or remove plant residues in
fall. Protect foliage in spring with a fungicide starting as soon as green shoots appear. |
Phytophthora blight
(Phytophthora cactorum) |
Young shoots turn black and die or
cankers appear along stems and cause them to collapse. Crown infections produce a wet rot that often destroys the entire plant. |
Favored by cool, wet conditions such as very heavy rains, excessive irrigation, and poor drainage. |
Grow plants in raised beds. Do not
overwater. Some of the fungicides effective against Phytophthora spp., such as mefenoxam, would probably be helpful. |
Verticillium wilt
(Verticillium dahliae) |
Plants wilt at flowering, but no
basal rots are present. The water-conducting tissue (xylem) in stems is
discolored. Infected plants may appear to recover, but symptoms will reoccur the following year. Fungus is systemic in plant. |
Disease is favored by cool, rainy
weather and hot weather at flowering. Water stress exacerbates the disease.
Fungus has a wide host range and survives for many years as microsclerotia in soil. |
Avoid fields where susceptible
plants such as tomatoes, cotton, strawberries, chrysanthemum, and others have
been grown. Fumigate soil with methyl bromide-chloropicrin mixture. Do not
propagate from plants that exhibit any symptoms of the disease. more info * |
| |
| Virus or viruslike disease |
Symptoms |
Host range and natural spread |
Comments on control |
Le Moine Disease
(cause unknown) |
Plants are dwarfed with many
spindly shoots that fail to form flowers. Roots of affected plants are often
irregularly swollen. The disease slowly spreads in plantings in a manner suggesting a soilborne vector. |
Plants are systemically affected and do not recover. |
Destroy infected plants. |
Ringspot
(Peony ringspot virus) |
A marked yellow mottle that is in
the form of chlorotic rings occasionally accompanied by small necrotic spots. Growth is probably reduced but not obviously. |
Virus is systemic in infected
plants. The virus is mechanically transmitted but little else is known about natural transmission. |
Destroy infected plants. |
| Peonies are
also susceptible to Armillaria root rot (Armillaria mellea),
crown
gall * (Agrobacterium tumefaciens), and Chalara
root and crown rot (Thielaviopsis basicola). |
| * For additional information, see section on Key Diseases. |
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