The purpose of spraying trees is to keep the trees healthy by preventing damage done by pests and diseases. Spraying increases the crop on fruit trees and prevents major damage to the tree to protect future crops. Many types of tree sprays help prevent insects and diseases from invading the tree in the first place. Other sprays help treat or get rid of an insect infestation or a disease affecting the health and growth of the tree.
Fruit trees are most commonly sprayed with various types of pesticides and insecticides since the invaders can damage the fruit crop. Preventative tree spraying typically takes place during the dormant season when the tree doesn't actively grow. Dormant oil is an example of a spray used during the dormant season. It smothers or kills the eggs and larvae of many insects that are damaging to trees, such as spider mites and aphids.
Other sprays, such as fixed copper and lime-sulfur, help prevent diseases on the trees before they develop. Tree diseases can affect the fruit and the branches themselves, causing them to die or otherwise suffer devastating damage. If not treated with spray, these diseases can kill the tree completely. Because fruit trees take several years to become established, spraying the trees protects the investment by supporting healthy growth of the trees.