| Also called red spot or measles, this disease affects
all aboveground parts of the peony. Caused by the
fungal pathogen, Cladosporium paeoniae, this
disease occurs each spring just before bloom. It is
mostly found on older varieties and is not
immediately lethal, though repeated bouts for
several years will affect plant vitality. It does not
cause early leaf drop or stem dieback but causes the
plant to be unsightly and lose its attractiveness as
spots coalesce to form blighted areas.
Symptoms and Diagnosis
Small, circular, red or purplish spots first appear
superficially on the upper surface of young leaves.
Later in the season they coalesce into large, glossy,
irregular, dark purple blotches while the underside
of the leaves becomes a dull chestnut brown. Short
reddish-brown streaks appear on the young stems
and petioles, and eventually the whole plant may be
affected with purplish or brownish red spots.
Life Cycle
The late-season blotch phase provides the
overwintering inoculum for the next year's infection,
especially in older varieties. Fungicides work only to
prevent infection; once the disease takes hold, there
is no treatment.
Integrated Pest Management Strategies
1. Remove debris. Be sure to remove all foliage to
ground level each fall and destroy. Infected debris
should not be added to the compost pile.
2. Apply fungicides. When the shoots are 2–4 inches
high and the weather is cool, overcast, and damp,
spray weekly with a fungicide until the flowers
open. Reapply following rain or overhead
watering. Mancozeb is currently registered for
controlling peony blotch.
3. Resistant varieties. Replant with newer resistant
varieties that are vigorous and thick-stemmed.
4. Watering and air circulation. Provide good air
circulation by proper spacing of plants and
foliage thinning to reduce humidity and promote
leaf drying. Water early in the day, so that leaves
dry thoroughly by night; drip irrigation is best. | 
