Safari, a systemic insecticide in the neonicotinoid class has much better action on armored scales than other products. The following is more information.
SAFARI (Dinotefuran)= New Armored Scale Control
Unlike Merit, the relatively new neonicotinoid insecticide named Safari (dinotefuran) has shown promise as an effective control against armored scales. Although both Safari and Merit (imidacloprid) have systemic capabilities with the same general mode of action, Safari is significantly more water-soluble. The high water solubility is thought to be the reason for the increased armored scale controls. Armored scales primarily feed by inserting their piercing-sucking mouthparts into parenchyma cells containing chlorophyll. Since Merit predominately moves through plants by vascular tissues (phloem and xylem), it does not readily enter into cells where armored scales feed. Consequently, Merit has not shown good efficacy against pests that feed within plant cells (typically less than 30-40% control). Recent University efficacy trials have shown dramatically improved results against armored scales with soil injection or drench applications of Safari insecticide. Although this material continues to be translocated by vascular tissues, it also appears to have the ability to permeate through cell walls and membranes. Some efficacy trials have shown controls exceeding 80%!
Information from Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the recent edition of the Plant and Pest Advisory from Rutgers University http://njaes.rutgers.edu/pubs/plantandpestadvisory/2009/ln070909.pdf