Prevention is always the best step in controlling diseases and insect pests. Spraying trees (especially fruiting ones) during the winter period (November through March) can help control pests and diseases that take up residence in cracks and crevices within the bark. Dormant spraying is more effective than waiting until the weather warms and pests and diseases become active. The following treatments have been shown to be highly effective in reducing both insect and disease populations of both conifer and deciduous trees. Apply spray oil in combination with an insecticide to kill overwintering eggs of aphids, psyllids, scale insects, mealybugs and moths. The oil acts as a suffocant while the insecticide kills existing adult insects that may still be living on the tree. Copper sprays are used to kill fungal spores. Copper is highly recommended on fruit trees where apple scab blossom wilt of cherries, peach leaf curl or leaf blotch diseases were particularly bad. Growers now believe that a dormant spray is key to protect against pests and diseases that would occur the following year.