Vigilance. The key to scales lurking in your landscape!

Scales are inconspicuous insects feeding on your trees and shrubs without notice until twigs and branches start dying.  Scales are sap sucking insects along with aphids, whiteflies, psyllids, adelgids, and mealybugs.  These insects all feed by sucking sap from the host plant.  Damage begins as a weakened look to the plant followed by branch dieback.  In severe cases plants are killed.  Scales produce a waxy covering over the top of themselves with their eggs making this insect difficult to control.  Scale infestations are exploding both in Colorado and throughout the United States.  Scales may be lumped into three types, armored, soft and pit. 

Armored
This scale class includes oyster shell, pine needle, euonymus, and juniper scale.  The most common is oyster shell so named for their waxy coating over the adult resembling a tiny 1/8 inch oyster shell.  These scales may be found on tree trunks and branches.  Pine needle scale is more common in mountain communities forming on spruce and pine needles.  Pine needle scale resembles white shells and a bit smaller than oyster shell.  

Soft and felt-like scales
Soft scales include striped pine and cottony maple scale, but their occurrence is sporadic. European elm scale (felt-like scale) is an ever present nemesis of American elm.  Adults are up to 3/8 inch in diameter, oval and grayish-brown with a white waxy fringe.  The overwintering stage forms on twigs with crawlers feeding on leaves.  One adult may lay up to 400 eggs!  A sticky residue falls from infested trees in spring and again in mid-summer.  

Kermes, pit and falsepit scales
Kermes scale occurs almost exclusively on red oak.  The scales resemble small tan spherical galls (1/4 inch in diameter) forming on twig terminals.  Damage is unique in that 3 to 4 scales form on twig terminals causing the new growth to fall.  Oaks are rapidly littered with dead branch terminals.  Falsepit scale is rapidly infesting ash and honeylocust trees in the Denver metro area.  Common falsepit scales are 1/6 inch in diameter, round and cream colored.  They are typically found in pits formed on the bark of the host in response to their feeding. 

Control
Early recommendations for scale control is to use a heavy oil spray (dormant oil) during the late winter or early spring months meant to smother insects.  In Colorado, this control method is limited by high solar irradiation that often breaks the oil down prior to successful control.  Spraying the affected plant when the scales hatch is also effective, but difficult on large shade trees.  Systemic insecticides applied at the plant base are also effective on select scale complexes.  Repeated insecticide applications are required for control. 

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