Ants are a frequent nuisance on fruit trees. According to the experts at the University of California, ants are likely attracted to the honeydew produced by aphids on the tree. They may also climb the tree to reach ripening fruit or sap coming from wounds in the trunk. You could apply shellac to each tree wound, but you would likely miss some, and you still wouldn't prevent ants that are trying to reach the honeydew or fruit. By stopping ants from climbing the tree, you can keep them away from your fruit and prevent them from boring holes in the wood, which can kill the tree.
Wrap the base of the tree with contact paper, making sure the sticky side is facing out. Ants will stick to the adhesive when they start to climb up the trunk.
Trim branches that touch nearby trees and structures. This prevents ants from reaching the fruit by climbing over from another tree or structure and forces them to climb up the base.
Replace the contact paper when it loses its adhesive properties. Insects, dirt and rain may affect the paper's stickiness.
Drench the soil around the tree with a chlordane spray available at garden supply stores. Chlordane is effective in killing ants quickly. It will also prevent ants from coming back for weeks or even months.
Try double-sided adhesive strips used to prevent cats from climbing onto counters. They are available at pet supply stores. Another option is to coat the base of the tree with motor oil or another sticky substance.
Avoid spraying the actual fruit tree with chlordane spray.