On July 31, 1998, at 1500 eastern daylight time, an Air Tractor AT-301, N3659T, piloted by a commercial pilot, was substantially damaged when it collided with mature corn and a ditch after it veered off a gravel road's left side shortly after touching down for landing. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 aerial application flight was not operating on a flight plan. The pilot reported no injuries. The flight had departed the same gravel road near Mentha, Michigan, exact time unknown. The pilot said his airplane's left wingtip collided with mature corn growing next to the road he was landing on when the airplane touched down. The on-scene investigation revealed the road's surface was uneven and covered with about 1/4 to 1/2- inch of lose gravel with hard-packed dirt underneath. Furrows in the gravel showed the airplane had turned about 45-degrees to the left shortly after touch down. The furrows were made by the airplane's main landing gear tires. The furrows continued through the ditch and into the corn where the airplane came to rest. N3659T's right wing was bent upward about 10-degrees beyond its normal dihedral angle. The right main landing gear leg had been pushed in toward the center of the airplane's fuselage. The leading edges of both wings had multiple dents ranging between 2 and 4-inches deep.