In some cases the best thing may be to prune out heavily infested branches. If the scale population is not too bad, a dormant oil can be applied once night-time temperatures remain above freezing. The oils may be sold as dormant oil, superior oil or horticultural oil. Be sure to follow label directions exactly. Complete coverage of all plant parts with spray is essential.
Oils kill by smothering the scale.
As the water evaporates, a thin film of oil forms over the scale and onto the plant surface. If this seal is complete, the scale can no longer get air and will die. If the coverage is poor, many scales will survive. Clyde S.Gorsuch, Extension entomologist.