| 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. Fuzzy 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. |
| 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 chloropicrin or a chloropicrin combination. Do not propagate from plants that exhibit any symptoms of the disease. |
| 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 black root rot * (Thielaviopsis basicola). | |||
| * For additional information, see section on Key Diseases. |