Tea scale is an insect that attaches itself to the underside of the leaves, as well as the stems. These insects suck the nutrients out of the plant which will cause discoloration and falling of leaves. When treating tea scale, you will want to use horticultural oil and mix with water. When applying the treatment you will want to hit every angle of the shrub, especially the infested areas. This insect will attach themselves, become stationary, and will not move again. When using an oil, this will suffocate the insect by clogging their breathing pores. If you have a heavy infestation, you will want to use horticultural oil followed by an insecticide, such as imidacloprid. A two prong approach will provide best results.