The pilot was spraying an agricultural field in an east/west direction but later changed to a north/south direction so as to avoid an agricultural airplane spraying an adjacent field. During the 15th pass over the field, the airplane struck a guy wire with its right wing tip that resulted in structural damage to its right wing. The pilot then flew back and landed the airplane without further incident at the airport where it was based. The pilot was uninjured. The pilot stated that he should have resurveyed the field after changing the direction of the passes over the field.