Peonies are a popular choice for many home gardeners. Their distinct foliage and large blossoms are a nice complement to other annuals and perennials. Yet, for everything that's right with a peony, a few things can go wrong with the plant. Fungal diseases rate high on the list, while some pests can bring their share of problems. Paying close attention and properly caring for your peony will likely help you to heed off these common problems, giving you more time to enjoy the plant.
Scales and thrips are the primary insects that present a problem to peonies. Look for scales in the summer on the plant's leaf bases and stalks. Scales are also often present during the winter below the ground area of the stalks. Most scales can be controlled by their natural predator, the ladybug, but if problems with scales persist, treat a peony with a dormant oil. Thrips can cause spots on peonies by sucking the juice from its buds, leaves and flowers. This pest can be easily controlled with a commercial insecticide.
Botrytis blight is the most common fungal disease that affects peonies. The disease can attack all parts of the plant and can occur at any time during the growing season. It is most likely to occur during wet, overcast weather. A sign of botrytis blight is patches of gray-brown fuzzy growth on the infected areas. When found, remove these infected areas from the plant as these spores can be transported by wind to infect other areas or neighboring plants. A second management option for botrytis blight is to treat it with a fungicidal spray.
Phytophthora blight is also a fungal disease that affects peonies. It can attack the stems, crowns, buds and leaves, causing the infected parts to discolor (turning brown to black) and sometimes also appearing leathery. Unlike botrytis blight, phytophthora blight does not produce any mold growth. Remove the diseased plant and its surrounding soil to prevent spreading the disease.
Leaf Blotch and Stem Spots
Also a fungal disease, leaf blotch produces reddish-purple lesions on stems and leaves. It is also common to see infected stems have reddish-brown streaks or spots. The best method for managing this disease is simply to remove the infected plant.