The pilot reported that, after completing an agricultural application flight, he returned to the airport. He added that, on final, he added flaps and became distracted by a spray handle that became open due to vibration. He took his hand off the control stick to close the spray handle, but because the airplane was improperly trimmed, the airplane pitched down severely. He pitched the nose up to about level, but the main landing gear struck the ground. The airplane bounced and impacted an irrigation system, the right main landing gear separated, and the airplane spun around before coming to rest. The airplane sustained substantial damage to both wings, the fuselage, and the empennage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.