Peonies are perennial ornamental flowers that grow between 2 and 4 feet tall depending upon the variety. They are generally hardy from USDA zone 8 to zone 2. Peonies suffer from several different pest problems.
According to the University of Rhode Island, scale insects are the most serious pest problem in peonies. Thrips, mealybugs and bulb mites also infest peony plants. In addition, peonies excrete a sweet nectar that attracts ants.
Female adult scales do not have recognizable heads, wings, antennae or any other evident body parts. Their shape varies depending upon the variety. Some scales excrete a nectar-like substance called honeydew. Thrips are narrow, slender, winged insects that grow to about 1/20 of an inch in length. Mealybugs are soft-bodied, wingless insects that form cotton-like clusters on plants. Bulb mites, which are 1/32 inch long, range in color from translucent white to brown.
Scales suck fluids from plants. A few scale insects are harmless, but large numbers weaken plant health. Thrips feed inside buds and damage plant tissue. Mealybug infestations stunt plant growth and cause premature leaf drop, while bulb mites destroy roots and stems. Ants do not help or harm the peonies; they are just attracted to the liquid.