How to Not Go Wrong with Peonies

Peonies are one of most popular cut flowers grown. Once you get past the initial establishment, they’re relatively easy to grow, and rewarding at any market.  With their long-lasting, colorful blooms, peonies are also popular with customers, and are frequently used in wedding bouquets and large floral arrangements.

A Maryland grower told me that the first year of peony production is waiting. The second year is additional waiting. The third year and every year after that, stand back, because peonies take off like a rocket.

Well, you know that an entomologist saying all these kinds of things about a plant is probably leading toward discussion of some group of insects that feed on those plants. I would not want to disappoint you, so let’s talk about one of the insects you’ll want to keep out of your peony production beds – armored scale.

Normally, we think of scale insects pest of woody plants. You would assume that since peonies are herbaceous perennials they could not support an armored scale population, but they can and do.

In October of 2012 I received a sample of peony stems covered with an armored scale. When I searched the literature I found that peony can be attacked by several armored scale species. The three most frequently found are prunicola scale, Pseudaonidia triolitiformis, peony scale, Pseudaonidia paeoniae (also called Japanese camellia scale), and fern scale, Pinnaspis aspidistrae. It is no surprise that these three pests originated in Asia, but have managed to spread across the United States, infesting many species of plants besides peonies.

Here is the uplifting part. You can prevent these scales from becoming problems in your production facility with a little monitoring and early detection, and safe insect growth regulator control materials.

Peony Scale 
Pseudaonidia paeoniae

This scale has been reported to kill branches if an infestation is allowed to build up. The female’s cover is what you’ll probably see since it is one of the largest life stages. It’s circular to oval, and highly convex; brown on the bottom, an orange to yellow center. It looks a little like a sunny-side-up fried egg with the white part being browned. The male covers are smaller, elongated and brown. With armored scale you can pop off the cover and expose the insect’s body underneath. The female scale’s body is yellow, and she is slightly oval. Work done by McComb and Davidson in Maryland in 1969 found one generation per year with crawlers in late May to mid-June. Males pupate in August, and mated females are what overwinters.  Pruning off old foliage with the scale on it and destroying the foliage is one of the best non-chemical sanitation methods. This pest can tolerate temperatures down to -15F  (Sel ‘Deshova, 1972)  so it’s pretty hardy in most parts of the United States. When crawlers are present in May, one of the better controls is to apply one of the two insect growth regulators, Talus or Distance.

White Prunicola Scale Pseudaulacaspis prunicola

The white prunicola scale went bonkers on the East Coast last summer.  The CMREC lab had never received so many scale-infested plant samples as it did in 2012. It is common on skip laurel and lilac, but is polyphagous, which means it feeds on just about anything. This includes peony, which we saw in October when we received a sample of peony with a heavy infestation of white prunicola scale.

Just like the peony scale, the females are circular and convex, but the difference is the female cover looks white and the center cap is yellow. Going back to my egg example, it would look like a sunny-side-up egg that Julia Child cooked: perfect white with an egg center. The males are elongated and bright white. The cluster of males will catch your eye.

This scale produces three generations per year here in Maryland, starting in May and continuing until fall. Don’t let this one build up on your peony or you will regret it. Use the same control methods as for peony scale.

Fern Scale Pinnaspis aspidistrae

This scale looks very different from the other two. The female’s light brown cover is elongated, and more oyster-shell shaped. Males are small and white-felted. We have received lots of samples of this insect on ferns, liriope, and mondo grass, but it thrives on peony. We have found two generations per year. In the second generation many of the females migrate down into the crown of the plant to overwinter, so removing old infested foliage many not wipe out a population. Watch for crawlers in May to June, and again August through September. Talus or Distance applied at crawler periods are effective control.

For most scale pests, an application of 3% horticultural oil in the spring when temperatures are 50-55F for at least a week should suppress a population.

If you find any scale on your peony plants, please email me a photo.

Prunicola scale on peony stem. The female cover is round and convex, like dinner plates stacked on each other.

Stanton Gill

Extension Specialist

Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]