magnolia scale

[Jordan]

The best treatment is horticultural oil applied in the early spring, at the crawler stage. The oil will smother active and recently settled crawlers. This horticultural oil is often called dormant oil, because it must be used before leaf or flower buds start to open but when temperatures are predicted to stay above freezing for 24 hours. It is important to read and carefully follow instructions when applying horticultural oil or any treatment.There is another window to treat for magnolia scale in late August, when the eggs hatch as crawlers. At that time, use horticultural soap or a summer-weight oil. Even if you applied dormant oil in spring, this summer application may be necessary to eradicate the scale


Source----http://articles.chicagotribune.com/2012-03-15/classified/ct-sun-garden-0318-qa-magnolia-scale-20120315_1_scale-insects-sooty-mold-crawler-stage