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Euonymus Scale

June 14, 2002

Euonymus scale, Unaspis euonymi, crawlers should be out on plants such as evergreen euonymus or pachysandra, their primary hosts in Illinois. Crawlers resemble tiny yellow spots that move around on leaves or stems. Stressed plants are more susceptible to attack than properly watered and fertilized plants.

Euonymus scale overwinters as a mated female on plant stems. Eggs develop beneath the scale and then hatch over a 2- to 3-week period. Most newly hatched crawlers that migrate on the stem generally start feeding near the base of plants. Crawlers may also infect other nearby plants by being blown around on air currents. Infestations often go undetected until damage is noticeable. Leaves become spotted with yellow or white areas. Plants growing near structures and along foundations appear to be damaged more than those in open areas with sufficient air movement. In addition, variegated forms of euonymus are more susceptible to attack than are green forms.

Heavy infestations can cause complete defoliation or death of a plant. Euonymus scale females are dark brown, flattened, and shaped like an oystershell. The males are elongated, ridged, 1/16 inch long, and whitish. Males are commonly found on leaves, females on stems and along leaf veins. There are two generations per year in Illinois.

Pruning out heavily infested branches is an effective means of quickly reducing the population. Avoid planting Euonymus japonica in landscapes as it is extremely susceptible to euonymus scale. Euonymus alata is resistant to the scale even when nearby plants are infested. Spraying a pest-control material in early to mid-June, when crawlers are active, minimizes problems later in the season. Pest-control materials recommended include acephate (Orthene), dimethoate (Cygon), insecticidal soap, and summer oil. Check plants regularly for crawlers. Four applications at 10- to 12-day intervals may be warranted.

Euonymus scale is susceptible to a variety of para-sitoids and predators, including lady beetles, green lacewing, and predatory mites. However, the natural enemies generally don't cause enough mortality to affect a large infestation.

Author: Raymond A. Cloyd


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