On August 6, 2004, at 0805 central daylight time, a Gruman G-164-B, N6677Q, sustained substantial damaged when it contacted a ditch and nosed over after it departed the end of a 2,400 foot grass airstrip near Bradford, Illinois. The commercial pilot was not injured. The 14 CFR Part 137 aerial spraying flight departed a grass airstrip near Fenton, Illinois, at 0740, and was landing at the grass airstrip near Bradford, Illinois, for fuel and chemicals. Visual meteorological conditions prevailed. No flight plan was filed. The pilot reported that he circled the grass airstrip once before setting up for a landing to the south on the north/south runway. He reported that he landed "as short on the north end as the railroad tracks would allow." He reported the brakes did not feel "as effective as normal." He pumped the brakes twice but they failed to slow the airplane. He reported that it was too late to "power-up and go around," and the airplane departed the end of the runway. The airplane hit a small ditch and it nosed over. A Federal Aviation Administration airworthiness inspector examined the airplane. He reported that the brake system was checked and it worked normally. He reported that there was nothing wrong mechanically with the airplane. A witness reported that he observed the airplane landing at the grass airstrip. He reported the grass was wet due to a heavy dew on the morning of the accident. He reported the final approach for landing was too high and the airplane landed past the first one-third of the runway. He reported the pilot "used up quit a bit of runway before he touched down." He reported that there was no way the airplane was going to stop on the runway due to the dew on the grass and the speed of the airplane.