Pine needle scale is a serious pest of pines throughout the state. It is most prevalent on Scots and mugo pine but is common on many other pine species as well. It is also found on spruce and hemlock and is likely to cause dieback on spruce. It is probably most serious to Christmas tree growers but commonly kills landscape plants as well.
Pine needle scale crawlers
Pine needle scale appears as elongate, white insects about 1/8 inch long on pine needles. There is a small, tan area at one end. Numbers commonly build up until the foliage appears whitish from a distance. In these high populations, branches and even entire trees can be killed. Pine needle scale overwinters as eggs. Eggs hatch into brick red crawlers as vanhoutte spirea is in full bloom. The crawlers, first-stage nymphs, roam on the foliage before settling down to feed and are susceptible to insecticide applications. They secrete a white, waxy substance that covers and protects the scale from desiccation, natural enemies, and insecticides. Over several molts under the waxy covering, the scale lose their legs, eyes, and antennae, becoming a protected sucking blob.
Adult legless females remain under their waxy coverings, but adult males emerge as tiny, two-winged insects. These exist only to fertilize the females, having no mouthparts, so they die after only a few days of not feeding. Mated females fill the area under the waxy covering with eggs and die. These eggs hatch into a second generation of crawlers that emerge when hills of snow hydrangea, Hydrangea arborescens ‘Grandiflora’, blossoms turn from white to green. Also, Queen Anne’s lace or wild carrot, Daucus carota, is in bloom at this time. This scale is susceptible to insecticide applications at that time as well. These scale grow throughout the rest of the summer, emerging as adults and producing eggs that overwinter.
Being an armored scale, these insects suck out the contents of individual cells and do not produce honeydew. Severely attacked foliage turns yellowish, eventually dies, and turns brown. It is common for this scale to be numerous on only one branch or one side of the tree. In landscapes, it tends to appear first on the side of the tree next to a building. On Christmas tree farms, only occasional trees may be infested or uninfested, depending on the severity of the infestation. When scouting, be sure to check all sides of a landscape tree, and be sure to check the entire field in a nursery or Christmas tree farm.
Application of acephate (Orthene), bifenthrin (Onyx, Talstar), cyfluthrin (Tempo), insecticidal soap, or summer oil should be effective if applied when the crawlers are active. One application is typically sufficient at this time of year although it is a good idea to apply two sprays of insecticidal soap or summer spray oil 7 to 10 days apart because they have so little residual effect. The second generation of crawlers emerges over a longer period, so any insecticide application should be repeated after 7 to 10 days. Realize that summer spray oil removes the blue bloom from Colorado blue spruce, leaving you with a green spruce.
Dead scale do not fall off of the needles. The easiest way to determine whether control is being attained is to look for scale on the current year’s growth once the needles that emerge from the candles have matured. Because of the late emergence of these needles, this is most effective as an end-of-season evaluation. You can also determine control with a hand lens or microscope. Using a needle, you can easily flip off the waxy covering to reveal the scale insect below it. Brown, shriveled scale are dead; plump, smooth scale are alive. Realize that a number of scale must be checked because dead scale from previous years will also be present.