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Know Before You Grow: Peonies Get Measles…What the Heck? | News, Sports, Jobs

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By Erik Draper and Joe Boggs

USO Extension

I was outside walking through Drapescape enjoying the colors and scents of the flowers, when I suddenly noticed that there seemed to be spots on the leaves of the peonies. Just had to take a closer look, of course, being the plant diagnostics devotee that I am! The symptoms were so classic and wonderful that I had to take a few moments to admire them! This disease goes by a plethora of names, including peony spot, red spot, stem spot, leaf spot disease, and finally, peony measles! The causal fungus, Graphiopsis chlorocephala, was previously known as Cladosporium paeoniae.

This fungus begins by infecting peony leaves, resulting in distinctive, shiny, purplish-brown circular spots or lesions on the upper surface of the leaf. On the underside of the leaf, those same spots are more of a milk chocolate brown color. However, later, as more leaf infections occur, the spots begin to coalesce or coalesce into spots, patches, or spots, as pathologists like to call them!

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While most infections initially start on peony leaves; however, they can also appear on young stems as individual raised spots. These spots on the stems will eventually coalesce and form what appear to be short, elongated, reddish-brown to purple streaks. These “miserable” spots and blemishes can also start to appear on flower buds, petals, and eventually, can even appear on seed pods!

One of the best ways to help yourself control this disease is to use sanitation! Since this disease overwinters in plant tissue, cut back and remove all above-ground plant growth, down to the soil line. Be sure to dispose of or destroy all plant debris and DO NOT COMPOST! It is the infected plant tissue from the previous year that serves as the main source of inoculum, releasing those fungal spores in the spring.

Peony measles most often affects older peony varieties, dwarf peonies and red peonies, which appear to be more susceptible to this fungal pathogen. Fortunately, this disease of peonies is simply a superficially unsightly aesthetic problem, rather than directly affecting the overall health or vigor of the plant. Many of the new varieties of peonies have shown increased resistance to peony leaf spot.

You can also improve the situation with some horticultural adjustments to how these plants are cared for in the growing season. When watering these plants, avoid overhead irrigation or wetting the foliage. Keep foliage dry by using drip irrigation or watering near the base of the plant as much as possible. If the plants are close to each other, create a space for air movement. You can selectively prune plants to improve air circulation, which will reduce the time it takes to dry leaf surfaces and stems.

If that does not improve the presence of measles in peony, fungicides can also be used to control this fungal disease. Simply protect new peony shoots with a properly labeled fungicide, and usually only one or two applications of the product are required. Carefully read and check the product label to ensure that not only is the application site (eg, garden, nursery, etc.) listed, but also that the peonies are not listed as sensitive to the product. Now you’re armed and ready to go out and slaughter those mysterious peony measles!

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Erik Draper and Joe Boggs are OSU Extension staff and authors of Buckeye Yard and Garden Line: https://bygl.osu.edu/.

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