Do not top evergreen trees. This destroys the growth habit of the tree. It is better to selectively remove limbs or remove the tree. When an evergreen tree is topped, most of the new growth is directed upward. After a few years the tree will become top heavy, then when a winter storm hits, it may become dangerous by breaking off and possibly falling through your roof or your neighbor’s. This is called the sail effect.
Just because pests such as aphids or other chewing insects are present does not necessarily mean that you have to spray pest control immediately. It takes a while but predators lag behind pest infestation. In other words, something often comes along and eats your pests!
First decide how much pest damage you or the plant will tolerate and then decide if action is required. Put chewing tobacco in an old nylon, let it soak overnight in your sprayer and then apply it in the morning. This will repel many chewing insects. Reapply after rain or as needed. See Master Gardener Plant Clinics.