Go the hardware or local nursery and look at what's available to deal with scale insects - but for housepants, not forests, orchards, etc.

You can use the same systemic product that's popular and used very effectively against scale insects on woody material in the landscape - Imidicloprid. Even though it's approved for indoor use, you shouldn't apply it as a spray anywhere but outdoors. After the spray has dried, the plants can be returned to the places they occupied indoors.

If you can spray the plant outdoors, Bayer Advanced 3-in-1 for insects, mites, and disease has a systemic insecticide (very effective on scale) - imidicloprid, and tebuconazole as a systemic fungicide, plus a miticide - tau-fluvinate (spelling ?) It's a very good product. If you can't spray because of outdoor temps, buy a product designed for use as a soil drench. It should have 1.47% imidicloprid as the active ingredient. Add 1 tsp/quart of water and drench the soil. Fertilome, Compare & Save, Optrol, are just a few of the folkd that provide imidicloprid for use as a drench.

My experience with products that deliver imidicloprid in granular form (Merit, Marathon, Dragon, .....) has been notable impact on root health of containerized plants, so I stick exclusively to the spray or soil drench.

...... hope that helps.

Al