Photo credit: S.D. Frank.
NC State Extension has published a very helpful article about Cottony Cushion Scales" by Steven Frank.
"Cottony cushion scale is an exotic pest that has been in the US for over a century. Initially a pest of citrus in California cottony cushion scale is now a pest of many crops including ornamentals throughout the southern US. It is quite generalist and feeds on many ornamental plants such as Nandina, Euonymus, Boxwood, Rose, and others. Today I went out looking for tulip tree scales on magnolias and instead found a severe cottony cushion scale infestation."
Since many of the plants it feeds upon are popular ornamentals - perhaps even in your own garden - you'll definitely want to read more at: