Treating the soil where scale infestation was present
I have removed eight cherry laurels that were heavily infested with scales. Perhaps they could have been saved, but we wanted a change in the garden. All roots were dug/pulled out and am now considering replacing with some type of holly bush. Should the soil be treated with an insecticide prior to replanting? Also, any suggestions for varieties of hollies as replacements would be greatly appreciated. Soil is not compacted, and is in partial to full shade in summer. Thank you ever so much.
You do not have to treat the soil prior to replanting. You have to match the plant to the site and you did not mention height and width of the shrubs.
Other considerations include: are deer an issue, windows in the location, etc.
You may want to take a photo and go to a large nursery for some recommendations and see what plants are available. There are many types of hollies, azaleas, rhododendrons, etc. They need good drainage. You may also be able to consider deciduous shrubs such as Itea.