When spring arrives in Michigan, our trees and plants come out of dormancy. Unfortunately, so do the bugs. Many of these insects feed on your trees and carry deadly diseases. Dormant oil is applied to deciduous trees and shrubs during the winter months when they are latent. It is made from refined petroleum oil and applied to the branches and trunks of trees. It is designed to protect them from damaging insects and destructive diseases without damaging the plant itself. It is a great way to boost the health and resistance of your trees and shrubs.