Too often, applications of dormant oils go on where scale insects are already dead. The following is an article on the subject.
Live vs. Dead Scale Characteristics:
Many professional landscapers and arborists will be applying early dormant oil applications against over-wintering insect/mite pests. Probably all too often, oil treatments are applied to scale populations that are not viable. Just a little bit of extra time is required to determine if the observed scales are dead or alive. Compare a live, viable scale insect to a water filled balloon. If the cover is somewhat flexible and soft to the touch it may still be alive. Furthermore, with the use of a sharp pinpoint (e.g., insect mounting pin), determine if insect body fluids are released. When the waxy cover of a live armored scale is removed from the plant surface, it will often appear as a red/yellow “blob of jelly.” As an example, by early spring pine needle scale females have already laid most of their red colored eggs and are probably dead (i.e., the female scale has become darkened, dry and shrunken in appearance). Pine needle scale eggs will hatch and red colored crawlers will emerge some time in May. As a side note, do not expect excellent controls of armored scales with the use of dormant oils. Some suppression may occur, but satisfactory results are not always achieved.
Article by Steven K. Rettke, Ornamental IPM Program Associate in the Plant and Pest Advisory, Landscape, Nursery, and Turf Edition, Rutgers University.
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