The pilot reported that during an agricultural aerial application run underneath electrical wires, the airplane’s right main landing gear collided with a signpost and was “torn off”. The pilot then flew the airplane back to his base of operations. During the landing, without the right main landing gear, the right wing impacted the ground. The airplane spun around 180-degrees before coming to rest in the upright position. The pilot was not injured; however, the airplane sustained substantial damage to the right wing during the accident.