Before commencing spraying operations, the pilot discovered that the left maingear tyre was deflated. The tube was patched, however about half way through the spraying task the pilot noticed that the tyre was partially deflated. Air was added to the tyre, and the operation was continued. On the last landing for the day the left gear commenced to vibrate and the aircraft veered to the left. The pilot was unable to maintain adequate directional control, and the aircraft entered the crop at the side of the strip before ground looping to a halt. The left main tyre was found to be flat.
