We have a mysterious infestation on our Hydrangea plants

Asked June 4, 2017, 9:40 PM EDT

We're attaching a photo to hopefully help you identify a mystery bug. They are on the underside of the leaves on our hydrangea plants in Portland. We took a leaf to some of the experts at Dennis' Seven Dees in Portland, they got out a photo-chart, and threw up their hands in wonder. Have you any idea what they might be, and how we can treat for them without harming bees?

Multnomah County Oregon insect issues hydrangea scale insects

2 Responses

Thank you for attaching the image. It reveals that your hydrangea has a serious case of cottony cushion scale. These particular insects infest far more plants than camellias, among them English ivy, euonymous, hydrangea, maple, mulberry, pittosporum, and rhododendrons.

Each small brown spot represents one insect, whereas each long white cottony mass is an egg case, each one filled with numerous eggs. Hatching time is often between mid-June and early July.

If the shrub is a reasonable size, you can start your management efforts by rubbing off every insect and egg case. At hatching time -- mid-June to early July -- follow up with a spray directed to the undersides of the leaves. The pesticides used for this purpose are quite safe when used according to label directions. Consider insecticidal soap, neem, or horticultural oil. (If you use an oil, choose one called superior- or supreme-oil as they can be safely applied during the growing season.)

As with all pesticides, read and follow directions. Also, don’t spray if the temperature is, or will exceed, 80 degrees Fahrenheit.

If the plant is heavily infested, consider replacing it with a healthy specimen.

This is not cottony cushion scale, but the close look-alike, cottony hydrangea scale, Pulvinaria hydrangeae. Best to ask your local extension agent for a suitable treatment option. Acetamiprid foliar treatments when the plants are not in flower is one option.