It sounds as though your euonymus has euonymus scale. Several species of scales attack euonymus. Heavy infestations cause leaf drop and may kill the plant. The insects overwinter as pregnant females. They lay eggs under their waxy white coating when temperatures rise in spring. Eggs soon hatch, and crawlers spread over the plant and begin feeding. You can spray the plants with dormant oil spray during the winter to kill the overwintering females. Thoroughly wet the stems and undersides of leaves. If the infestation is severe, cut the plants back near ground level in spring, and spray the new growth with an insecticide to kill the crawlers.