The trick lay in developing unique mixtures of psychoatives and contaminants capable of degrading so-called "condemned" food stocks so clearly that anyone in relative proximity to the caches knew damn well that the foodstuffs had indeed intentionally been debased, and as such would not be edible or fit for human consumption or food production.
Inventors William H. Collins, Vincent J. DiPaola, and Louis M. Sherman were the first ones to constuct a spray gun which made foodstuffs inedible by kicking up waves of "drunkeness filled with fantasy and exaggerated images."
Here's how the technology workes. Just about every cocktail pumped into the spraying gadget is made up of at least one psychoative agent, sometimes more. Collins, DiPaola, and Sherman cite numerous chemicals, including LSD. Apparently, researchers consider it to be ideally suited for debasing condemned food reserves. 
So there is no Holy Grail. The sky was the limit, but came in different colors, smells, and tastes.
It doesn't take a skilled marksmen to handle the device. Collins, DiPaola, and Sherman fashioned their device to be carried and utilized "more conveniently in the manner of a gun," not a hulking cannon. The thing was optimized for destroying stored foodstuffs very quickly, with few agent formuations, and with minimal manpower.
This is where the tale of the Army's psychoactive squirt gun really gets interesting. Cached foods were crucial to uprisings and the success of insurgents. As the researchers put it:
"Terrorists and insurgents must have food on which to subsist. Since grains such as wheat or rice make up the greater portion of the food consumed daily, uprisings may be quelled by spoiling the stored grains."
In this sens, it seems that the US Army figured the best method of anti-terrorist warfare - at least it wouldn't kill them.
 Voice of Russia, Vice