http://en.wikipedia.org/wiki/Fort_Detrick

"
(...)
According to Randal Curtis, U.S. Army Corps of Engineers - St. Louis District, who compiled the report, herbicides generally were applied with hand sprayers, and using portable shelters to prevent overspray of chemicals from one plot to the next, which would have invalidated the tests. (...)"
http://www.globalsecurity.org/military/library/news/2012/05/mil-120501-arnews03.htm

If this report relates to the Cadmium Sulfate spraying in St. Louis remains unknown. There is only one exact product mentioned: 2,4,5-T

On the other hand: maybe because the U.S. Army Corps of Engineers is stationed in St. Louis District this maybe the reason why the Cadmium Sulfate Spraying has taken place in St. Louis, Missouri.

One has to put it that way: In Fort Detrick they are developing military ideas, in St. Louis they are thinking how to transfer those ideas of Fort Detrick into practical manageable ways - the task of engineers. And that maybe the reason why this report was compiled in the St. Louis District and not at Fort Detrick.