Agent Blue is a herbicide, similar to Agent Orange, used by the United States during the Vietnam War. It was sprayed on rice paddies and other crops, in an attempt to starve the Vietnamese of valuable crops.

As rice is incredibly durable, and difficult to destroy with conventional explosives, and does not burn, the weapon of choice was herbicides.

Agent Blue affects plants by causing them to dry out. As rice is highly dependant on water to live, using Agent Blue on these paddies can destroy an entire field and leave it unsuitable for further planting.

Agent Blue is a 2:1 mixture by weight of Na-Dimethyl Arsenate (Na Cacodylate) and Dimethyl Arsenic (Cacodylic acid).

Today, large quantities of the chemical named Agent Blue are still used on lawns and crops throughout the country.

Taken from ZNet Ecology:
"Arsenical herbicides containing cacodylic acid as an active ingredient are still used today as weed-killers. In the US they are used extensively, from golf courses to backyards. They are also sprayed on cotton fields, drying out the plants before harvesting. So common -- and so profitable -- is the original commercial form of Agent Blue that it was among 10 toxic insecticides, fungicides and herbicides partially deregulated by the US Environmental Protection Agency (EPA) in February 2004. Specific limits on toxic residues in meat, milk, poultry, and eggs were removed."