The pilot reported that he saw the power lines at the north end of the field as he started the aerial application work. However, he reported that he did not conduct a detailed observation of the lines. The power lines encountered during the accident flight had two lower wires that he did not anticipate. The arrangement of the power lines was different from those he had encountered in the area previously. As he approached the north end of the field, he was concentrating on a small group of trees when the airplane impacted the lines. He stated that the two lower wires caught him completely by surprise. The windshield separated as a result of the impact and he had difficulty seeing because of debris and wind in his eyes. He subsequently elected to dump the application load and execute a precautionary/forced landing to an open field. The pilot reported that there were no anomalies related to the airplane prior to impacting the wires. The airplane sustained substantial damage to the wings and during the landing.