Black aphid-like insects attack only conifers. Like aphids, they are sap-sucking and on some species of spruce can cause galls to form. On most other conifers they move around the plant and are usually covered in a fluffy, white waxy substance.
Bad infestations can cause the foliage of the conifers to yellow but generally the trees will continue to grow fairly well.
It is very difficult to spray large trees and the pests are usually tolerated by the trees themselves.
Chemical - If the conifer is small enough some protection can be given by spraying with a systemic insecticide during mild, dry weather in February, such as Bug Clear concentrate. The overwintering adelgids aren't covered in the waxy coating so are more vulnerable to chemical sprays.
Organic – spray with a soapy water solution or horticultural oil also in late winter.