Peonies are remarkably resistant to pests and diseases. Among insects, thrips represent the only cause for concern to the health of the plant. Ants are often found on peonies, but they pose no threat apart from their potential to spread fungal disease.
Adult thrips are tiny winged insects and very hard to see. Cylindrical in shape, they are slim and may be white, yellow, brown or black. They are sometimes referred to as "thunder flies." The larvae resemble adult thrips without wings. The adults’ wings appear to have a fringed effect.
Thrips feed in large numbers on the upper sides of leaves, as well as on the flowers and buds. This causes a silvery, mottling effect and some distortion. Puncturing the petals to feed on the plant juices causes discoloration. Thrips pose a particular problem for white, yellow and lighter colored blooms.
Infected buds and leaves should be removed and destroyed. Thrips often bury deep into the leaf or bud, so spotting an infestation early makes control more effective. Thrips can be washed off leaves. Keeping the plants misted may prevent an attack as thrips prefer a dry environment.
The peonies’ buds produce a sticky, sugary substance that runs down the stem of the plants and attracts ants. Contrary to popular belief, however, ants are not required to help the flowers open.