Hi Keith,
First I'd like to say that your plant appears to be a yucca and not a dracaena. If the edges of the leaves are serrated and feel rough, then you have a yucca.
http://www.evergrowing.com/tips/yucca.htm

I don't use toxic chemicals like Malathion and don't recommend them. I would suggest that you use a horticultural oil. The timing of the application is important. From this site:
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7408.html

"Spring/Summer Treatments. Dormant season applications of oils are not appropriate for scales on citrus or avocado because these trees do not enter a winter dormancy; oils are best applied to these trees in spring or summer. Horticultural oils can also be used in spring or summer against scale crawlers on deciduous plants. Treatment at this time requires more spray volume than a dormant treatment because foliage as well as bark must be thoroughly covered. Spring or summer applications must be carefully timed to reach crawlers, which are the most susceptible stage. Use traps made of double-sided sticky tape to determine when crawlers are hatching. Before crawlers begin to emerge in spring, tightly encircle several twigs or branches on the infested tree with transparent tape that is sticky on both sides (this tape is available at stationery stores). Change the tapes at regular intervals, about weekly, and examine the tapes with a hand lens to identify the crawlers. Once eggs begin hatching, scale crawlers get stuck on the tapes and appear as yellow or orange specks."

Newt