Scale insects are some of the most important pests affecting conifer trees and shrubs in Colorado. As scales feed on bark and needles, they remove sap and damage cells. This can lead to decreased vigor, needle drop and dieback in the plant, and increased susceptibility to other insects or disease. Some scales also excrete sticky honeydew, which further detracts from plant appearance and attracts nuisance bees and wasps. There are several important scale insect pests in Colorado yards. Pine-needle scale has long been the most damaging species; however, the striped-pine scale has become a serious pest along much of the Front Range. Several additional species are of minor or occasional importance. The best time to prevent or get rid of scale insects is during the “crawler” stage from mid- to late-spring, which lasts one to two weeks by using the insecticides Sevin or Malathinon. In addition, summer or dormant oils can be applied to control crawler and adult scales. For more information on identifying and treating scale insects see PlantTalk script Scale Insects on Pines, Scale Insects Affecting Conifers, Insect Control: Horticultural Oils, and Oystershell Scale on Woody Plants.

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