Water in systemic insecticide

Is there a systemic insecticide available that can be watered in and taken up by the root of a house plant rather than sprayed on? My conservatory plants (Yucca, Ficus, Draceana and several others) are slowing succumbing to Scale and despite repeated spraying with an indoor bug spray its doing nothing and the problem is getting worse. I have taken plants outside and gave them a good wash with garden hose several times during summer. Some of the plants are several years old and are otherwise healthy and huge (yucca is nearing 8 foot tall!!). Don't really want to lose them although getting to the point of thinking I'm going to have to get rid of them and start afresh once I've given the conversatory a deep clean to rid of any remaining Scale insects lurking. The only otger thing I could think of is a insect fogger like the ones that kills fleas, but not sure how e it would be on Scale insects.