Dormant spray should be applied to all deciduous trees and shrubs which had insect infestations or disease during the prior year. This is especially important for fruit trees and roses. Dormant oil spraying should be done on a clear day when there is little or no breeze. The ideal temperature for application is between 40 and 70 degrees F., preferably temperatures should remain over 50 degrees F. for at least twenty four hours in order to get the oil to spread out over the tree and cover all crooks and crevices.
Complete coverage is required for effective control of all overwintering pests.
In some instances, gardeners are successful with only one application during the period of early December through late January. But if the infestation or disease was very bad during the previous season, two sprayings would be the best bet. For insect control, use Dormant Spray Oil or Volck Oil. These oils will smother insect eggs overwintering in the same places as the fungal spores. Either of these two products can be mixed together with Lime Sulphur for excellent control of insects and disease.