White Scale Diseases on Plants

White Scale Types

• The pine needle scale is among the white scale types with oval, elongated, white 3-mm-long bodies. Common hosts of pine needle scale are Douglas fir, hemlock, pine, fir and spruce. Scurfy scales commonly infect crabapple, all varieties of plants in the Prunus spp. group, apple and many deciduous landscape plants. Scurfy scales are 3-mm-long, pear shaped, flat and dull white in color. The female juniper scales are dirty white in color and have yellow centers. The males are all white and smaller than the females. Juniper scales are commonly on arborvitae, junipers, cypress and incense cedars.

Life Stages

• Many scale species do not require a male to mate in order to produce eggs. Mature females produce eggs that are hidden under her body. These eggs hatch into very small, mobile crawlers that are mostly yellow to orange in color. Crawlers are able to walk on infested plants and often spread to other plants by winds or birds. Within a day or two, the crawlers find a spot to settle down and become immobile as they feed and grow.

Damage

• Scales have long, threadlike mouths called stylets that are nearly a sixth to and eighth the size of the insect body. The insects suck out plant sap by inserting the stylets into plant cells. Damage leads to a slow decline in plant health and poor growth. This causes dieback of branches and twigs. Weaker hosts are likely to die entirely from damage. As the pests feed, they secrete sticky honeydew that invite secondary pests like ants and wasps and promotes the growth of sooty black fungus in infested tree areas.

Control

• Introduce natural predators such as small parasitic wasps and lady beetles in infested trees to control the number of scales on trees. Spray the trees with dormant oils just before bud break between late March and early April to reduce chances of infestation later. Time the application of insecticides to catch pests in their crawler stage as soon as they hatch for most effective control. Recommended insecticides include horticultural oils and insecticidal soap.