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Euonymus Scale

Susceptible Plants
Wintercreeper (Euonymus fortunei), European euonymus (Euonymus europaeus), pachysandra (Pachysandra terminalis), bittersweet (Celastrus scandens)

Description & Symptoms
Euonymus scale is part of a group of insects referred to as armored scale. Armored scales live under a protective covering and feed on plant juices. Euonymus scale appears on the stems and leaves of infested plants as tiny white lines 1/16 inch long or as slightly larger, swollen brown lumps. Heavily infested plants may be coated with tiny white lines, particularly on stems and leaf veins. This coating of white lines is the most easily identifiable symptom. White or yellow spots appear on leaf surfaces in response to scale feeding.

Timing & Life Cycle
Euonymus scale spends the winter as a mated adult female that then lays eggs in the spring. These eggs hatch into tiny immature scales called crawlers that, for a brief period, move along stems and leaves until they become immobile, grow a protective covering, and begin to feed. The first crawlers hatch and are active from late May to early June. Another generation of crawlers is active again from late July to August.

Small yellow or white spots appear on upper and lower leaf surfaces. The entire leaf may turn yellow. In severe cases, leaves drop and the plant dies.

Treatment & Solutions
If possible, site plants where there will be good air circulation. Scale tends to be worse in plants growing close to buildings. In light cases, infested branches may be pruned out and destroyed.

Horticultural oil may be sprayed on plants to smother euonymus scale. Timing is critical in the treatment of scale insects, all of which have some type of protective covering. Dormant oil should be sprayed in late winter or very early spring to smother the females before they lay eggs. Dormant oil must be applied when temperatures will be above freezing for 24 hours for deciduous plants and above 40 degrees for evergreen plants. Once plants have started to leaf out or bloom, dormant oil should not be used.

Summer-weight oil, a lighter solution of horticultural oil and water, is used against newly hatched crawlers. It should be applied in late May and early June and again in late July and August. The spring treatment can be applied at the time catalpa trees are in bloom, which generally coincides with crawler activity. It is important to carefully follow directions on the bottle when applying oil. 

For more information about chemical treatment of euonymus scale, call the Plant Information hotline at (847) 835-0972.