The blooming of beautybush, Kolkwitzia amabilis, throughout portions of Illinois indicates that Euonymus scale, Unaspis euonymi, crawlers should be out and about on plants such as evergreen euonymus or pachysandra--their primary hosts in Illinois.
Crawlers resemble tiny yellow spots that move around on leaves and stems. Stressed plants (as with other insect and mite pests) are more susceptible to attack than plants that are receiving proper irrigation and fertility.
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. Many of the newly hatched crawlers that migrate on the stem generally start feeding near the base of plants. Crawlers may also infect nearby plants by being blown around on air currents. As a result, infestations often go undetected until populations and damage are noticeable. Leaves become spotted with yellow or white areas. Plants that are growing near structures and along foundations appear to be more susceptible than those in open areas with sufficient air movement. In addition, variegated forms of euonymus are more susceptible to attack than are the green forms.
Heavy infestations of euonymus scale can cause complete defoliation or death of a plant. Euonymus scale females are dark brown, flattened, and shaped like an oystershell, whereas the males are elongated, ridged, and white in color. Males are commonly found on leaves, whereas females are located 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 because it is extremely susceptible to euonymus scale. Euonymus alata is resistant (or tolerant) to euonymus scale even when nearby plants are infested. Spraying an insecticide in late May through early June, when the crawlers are active, can minimize problems later in the season. Insecticides recommended for euonymus scale include acephate (Orthene), insecticidal soap, and/or summer oil. Be sure to check plants regularly for the presence of crawlers, which can help to time insecticide applications. Four applications at 10- to 12-day intervals may be warranted, depending on the infestation level.
Euonymus scale, like many scale species, is susceptible to a variety of natural enemies, including parasitoids and predators. These include braconid and ichneumon wasps, lady beetles, green lacewing, and predatory mites. However, natural enemies generally don’t cause enough mortality to affect a large infestation.