The pilot reported that on approaching the paddock to be sprayed he did a circuit to observe wires and obstructions. He observed two sets of wires, one set running along a main road and another set running along one side of the paddock to a bore. The pilot decided to carry out some clean up runs along the bore wire first, to make the spray runs on the paddock safer. On the fourth run the pilot was intending to go over the road wires, but the landing gear snagged them, and brought the aircraft down to the ground some distance away. The pilot stated that there was a crop of tall sunflowers growing in the corner of the paddock, which made it too dangerous to go under the wires.