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Euonymus scale, Unaspis euonymi (Comstock), is an exotic armored scale of Asian origin that feeds on the foliage and stems of woody landscape plants in Pennsylvania. It has become a major concern in many landscapes because, without treatment, heavy scale infestations will reduce photosynthesis, stunt plants, cause leaves to abcise, and kill all or part of the plants.
The maleâ€™s white, narrow, waxy cover is about 0.8 mm long (Fig. 1a). Adult males emerge as tiny wasp-like insects. The waxy cover of a mature female is approximately 2 mm long, grayish-brown, flattened, and pear-shaped . The crawler stage of this key pest is about 0.3 mm long and yellowish-orange.
Life cycle:The male scales are white, long and thin. They occur in the greatest numbers on the lower branches and leaves of the plant. Their conspicuous white color on the green underside of leaves is the best signal that this pest is present. The female Euonymus scales are brown, wider than the males, and are found on stems and only occasionally on leaves. They are about 1-2 mm (1/16 inch) long.
The eggs are deposited under the female scale cover and begin hatching in May. The young scales, called crawlers, appear as yellow specks smaller than a pin head These small crawlers move to leaves or stems and begin feeding by piercing the plant tissue with thin, thread-like, microscopic mouthparts. They quickly begin producing the hard protective covering which they extend backwards as they grow.There are two generations of Euonymus scale produced in Delaware. The hatching time of the second generation is not clear cut, however, and the two generations overlap. All stages are present in the summer, but crawlers are most abundant in May and August.
Damage:The first visible damage is yellow spotting on the leaves. Variegated forms of Euonymus sometimes exhibit a pinkish-red color in the leaves. On heavily infested plants, thousands of mature female scales encrust the stems and reduce photosynthesis. This results in stunted plants and leaf drop, and can kill all or part of the plant.This key pest causes injury to host plants by removing fluid from non-vascular plant cells. It does this with its piercing-sucking mouthparts that results in a reduction of plant health and yellowish stippling or spotting of the foliage. Heavy infestations may occur on twigs or leaves that can cause defoliation of the plant. An infestation of this armored scale may result in twig dieback or death of the plant.
Control:This pest is most difficult to effectively manage at the base of infested plants near the ground. This is especially true with various vine types of euonymus.To reduce populations of first generation crawlers, apply a registered insecticide according to label directions during late May through June. Second generation crawlers should be managed with applications made during late July through August. Prune and destroy heavily infested branches or twigs when indicated.The lady beetle, Chilocorus kuwanae, was introduced several years ago in the eastern United States to assist with the management of euonymus scale. This lady beetle is 3- 4.5 mm long, black with two red spots on its wing covers.
Avoid use of Euonymus japonica, a very highly susceptible plant variety to scale attack. Use fast-growing varieties and mulch and water, especially if drought-stressed, to aid the plant in fighting scale infestation. Plants in the shade will less likely be attacked then those in full sun. Severely trim back heavily infested material and protect new growth with oil. A newly released lady beetle, with 2 red spots on black wing covers shows promise as a biological control for Euonymus scale. Avoid insecticide spraying to aid this beneficial insect.
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