Euonymus scales have three stages to their life cycle - egg, nymph and adult. The adult overwinters as mature fertilized females. Adults are very difficult to control with an insecticide due to their protective coating. In early spring, prior to leaf bud break, it is possible to apply Horticultural Oil in a mixture to the plant, and by so doing, suffocate the insect inside their waxy shell. If you have missed this opportunity, then the next opportunity to control euonymus scale is in late May or early June over a period of 2-3 weeks as the eggs hatch and the nymphs (which are also known as crawlers) crawl to a new location to feed, or are blown by the wind to adjacent vulnerable euonymus. This same lifecycle can repeat itself in mid-July. The crawler stage is the most vulnerable to control by an insecticide. Crawlers are very small and orange-yellow in colour.

As the timing of when to check is important, there are a couple of marker plants that will help you to know when to check. When Ivory Silk Tree Lilacs or Catalpa trees are beginning to bloom would be the best time to check. If you know you already have scale on your euonymus put a small piece of black electrical tape on the branch above where the overwintering bumps are. When the crawlers start to crawl upward toward the leaves, they will stick and show up well against the black tape background.

When Ivory Silk Tree Lilacs like this one are in bloom, that's the time to check for Euonymus scale crawler activity.