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Euonymus Scale

This armored scale from Asia is a serious pest of euonymus throughout the United States and Canada.

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NAME: Euonymus Scale (Unaspis euonymi)

Fertilized females overwinter on the stems and leaves of host plants. In early spring, when new leaves emerge, they lay yellow elliptical eggs and die. The eggs hatch over a two- to three-week period. The young scales, or crawlers, which look like specks of yellow-orange dust, travel along the stems and leaves of the host plant or are windblown. They eventually settle down, inserting their long, needlelike mouthparts into plant tissues to suck sap, and they develop a waxy protective covering.

The gray to brown, oyster shell-shaped females are typically found on stems, while the fuzzy, white, elongate males are typically found on foliage. They reach adulthood within 40 to 60 days. Males mate with the immobile females to produce a second generation.

Generally, there are two generations per year in the northern and central areas of the United States, and three or more in southern areas.

SYMPTOMS: Yellowish or whitish spots or halos on the upper surface of the leaves are caused by feeding males. The females can often be seen clustered on petioles and stems. Leaves of infested plants yellow and drop prematurely, often leaving tufts of foliage at the ends of stunted branches. Heavy infestations lead to plant death.

CONTROL: Apply horticultural oils to dormant shrubs in late fall or early spring, when temperatures will remain above freezing until the spray dries. During the growing season, apply horticultural oil or insecticidal soap when the mobile crawlers are present and when they have recently settled.

To determine when crawlers are active, attach double-sided sticky tape to twigs or branches and examine the tape with a hand lens for the presence of yellow-orange crawlers. Change the tape at weekly intervals. Alternatively, shake a branch over a white sheet of paper and look for moving orange specks.

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