From MSU Extension:
Magnolia scale (Neolecanium cornuparvum, Thro) is the largest scale found in the United States. Its primary host is magnolia. Star magnolia, saucer magnolia, cucumber tree and lily magnolia are among the species most commonly infested. Like other scale insects, it is good at disguising itself to escape detection, but its large size – up to 0.5 inches – makes it more conspicuous. Scale insects often resemble small galls, plant parts like buds or lenticels (pores for gas exchange), or seeds. Adult male scales are small, active and superficially resemble tiny flies. Adult female soft scales are comparatively large and sedentary with sac-like bodies that are often covered with wax.
According to Michigan State University Extension, small infestations can be removed any time of year by pruning out infested branches. Magnolia scale is now at the stage where it is producing crawlers, the stage most vulnerable to control. Horticultural oils, often called summer oils, applied after the crawlers have emerged in late August can be very effective in reducing the scale population. Be sure to obtain good coverage. Oils can be applied in fall before freezing weather and again in early spring before the flower buds swell to kill the overwintering nymphs located on the stems. Crawlers or newly settled crawlers are also vulnerable to a variety of other conventional insecticides.
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