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.

Organic Strategies

Strategies 1, 3 and 4 are strictly organic approaches.