A shiny spot of honeydew may remain where the scale was attached. If you need further confirmation, take a close look and you'll see legs and antennae attached to the shell. Soft scales are difficult to control. The adults can be picked off by hand or with a pair of tweezers. Small populations can be killed using the cotton swab and rubbing alcohol treatment described for mealybugs.
Insecticidal soap is effective on the crawlers or young scales.
It is less effective against the adult scales. Adult females will lay eggs under their body. This causes them to raise up off the plant. Use your magnifying glass to time your insecticidal soap application so it coincides with the time when the crawlers are most active and present in the highest numbers. Insecticidal soap kills only by direct contact with the insect.