It would appear that the new pesticides are much more potent, and we did have trouble with Furadan in the past in sweet corn areas. Even though Furadan was a really bad poison for us—it knocked the bees just about as bad as this stuff—it was over in a couple of days.
The poison they're using now has a shortest half-life of 107 days, and according to the research, they're finding it in the soil 18 to 19 years later. The neonicotinoids are the most easily translocated poison there is. It will translocate and flow with the subsoil moisture, so it's going to naturally flow to the lowest spots.