If your trees or shrubs suffered badly from insect attack this year (e.g., aphid, scale, red spider mite, etc.), then there is an extremely high probability that they will be back next year in far greater numbers.
This is because most of these insects live for only one year. Consequently, towards the end of the growing season they lay their eggs just under the bark or in bark cracks or fissures, which are not visible to the naked eye. When spring arrives, the eggs hatch and the newly born insects continue where their parents left off the following year.
This problem can, however, be controlled during the winter by applying a winter wash. Winter washes are based on a biodegradable oil derived from oil seed rape that is applied to fully dormant trees as a spray or brush that kills overwintering eggs of, for example, aphids, psyllids, scale insects, mealybugs, and moths. Winter washes also have the advantage of that they will kill unsightly growths of mosses and lichens on tree trunks and twigs. Consult your local Bartlett Tree Experts Arborist for further advice.