I have a yew hedge that is infected with Cottony Camillia scale. Is it...
Typically, the female cottony camellia scale insects have died by now and most have fallen off the shrub leaving white ovisacs behind.. The immatures remain on the underside of the leaves through winter. If we have a couple of cloudy days with daytime temperatures below 82 degrees, you could spray the shrubs with insecticidal soap or horticultural oil diluted to the summer rate. It is also appropriate that you spray again with dormant oil during the dormant season (Dec - Feb). An optional tactic would be to apply a systemic insecticide such as imidacloprid to the soil in early spring.
Normally, yews can be trimmed at any time, but if the shrubs are under stress from the scale infestation, it may be better to wait until the dormant season to do any heavy pruning.