White egg sacks on Japanese maple
Nonresidual, Contact Insecticides
"Where plants can be sprayed, complete spray coverage of infested plant parts with horticultural oil at the proper time provides good control of most scales. Horticultural oils (e.g., Bonide Horticultural Oil and Monterey Horticultural Oil) are specially refined petroleum products, often called narrow-range, superior, or supreme oils. Other nonpersistent, contact sprays for garden and landscape plants include insecticidal soap (Safer Brand Insect Killing Soap Concentrate II), neem oil (Bayer Advanced Natria Neem Oil Concentrate, Green Light Neem, Garden Safe Brand Neem), canola oil (Bayer Advanced Natria Multi-Insect Control), and other botanical (plant-derived) oils.
These insecticides have low toxicity to people and pets and relatively little adverse impact on the populations of pollinators and natural enemies and the benefits they provide. To obtain adequate control, thoroughly wet the infested plant parts with spray, typically shoot terminals and the underside of leaves. More than one application per growing season may be needed, especially if the targeted pest has more than one generation a year. Thorough spray coverage is especially critical when treating armored scales and oak pit scales as these scales are generally less susceptible to pesticides than soft scales."
This section tells you how to make and use a tape trap:
Transparent double-sided sticky tape can be used to effectively time a foliar insecticide application. During the spring before crawlers begin to emerge, tightly encircle each of several scale-infested twigs or branches with transparent tape that is sticky on both sides, available at fabric or craft stores. Double over the loose end of the tape several times to make it easier to remove. Place a tag or flagging near each tape so you can readily find it. Change the tapes at weekly intervals. After removing the old tape, wrap the twig at the same location with fresh tape. Preserve the old sticky tapes by sandwiching them between a sheet of white paper and clear plastic. Label the tapes with the date, location, and host plant from which they were collected.
Scale crawlers get stuck on the tape and appear as yellow or orange specks. Examine the tape with a hand lens to distinguish the crawlers (which are round or oblong and have very short appendages) from pollen and dust. Use a hand lens to examine the crawlers beneath mature female scales on bark or foliage to be certain of crawler appearance. Other tiny creatures, including mites, may also be caught in the tape.
Visually compare the tapes collected on each sample date. If a spring or summer foliar insecticide application is planned, unless another time is recommended for that species, spray after crawler production (abundance in traps) has peaked and definitely begun to decline, which is soon after most crawlers have settled."