Willow scale, whose primary host is aspen and cottonwood, is a relatively new insect to Colorado. These grayish-white, oval shaped, immobile insects suck sap through the thin bark of the host tree's branches and trunk. Damage often results in the death of infected trees, either directly due to the scale or through secondary infection by cytospora canker. Treatment depends on the severity of the infestation. Options range from sprays with a horticultural oil to applications of a systemic insecticide.
PHOTOS (middle/right) accredited to: W. Cranshaw, CSU, www.Bugwood.org