Anticrop Biological Weapons Programs - Deadly Cultures: Biological Weapons Since 1945 - page 217

were directed to developing a chemical agent that would, at very low
concentrations, be effective in reducing the yields of both narrow- and
broad-leaved crops. Investigations in this area included the screening of
some 200 potential anticrop chemicals per month and resulted in the
standardization of a number of agents that would see use on an unprece-
dented scale in Southeast Asia in the later 1960s.
Investigations by the Biology Branch centered on those agents that, ac-
cording to one declassified source, “offered the greatest potential in the
attack of [on] food crops.” Investigations addressed a wide variety of
problems related to the large-scale production, storage, stockpiling, and
military use of three agents: the causal agent of stem rust of wheat (Puc-
cinia graminis), codenamed TX; the causal agent of rice blast (Piricularia
oryzae), codenamed LX; and the causal agent of late blight of potatoes
(Phytophthora infestans), codenamed LO. Two additional agents are known
to have been produced and standardized, but their identities are not
known. A 1969 summary of biological operations, antipersonnel agents,
antiplant agents, and munition systems listed TX as “ Puccinia graminis var.
tritici Erikss. & E. Henn., race 56,” with an infection dose of just 0.1 gram/
acre or 1 pound for 10 square miles, with spores remaining viable in aero-
sol form for several days. 24
Other agents under review at this time for their potential as anticrop
biological warfare agents included the causal agent of stripe rust of
wheat, Puccinia striiformis West; the causal agent of Hoja Blanca of rice,
Hoja Blanca virus (transmitted by the leafhopper Sogata orizicola ); the
causal agent of bacterial leaf blight of rice, Xanthomonas oryzae Uyeda and
Ishiyama; and the causal agent of downy mildew of poppy, Peronospora
arborescens —the last reflecting an increase in Chemical Corps interest in
the 1960s in developing such agents for use against illicit narcotic crop
production.
A number of these saw development and eventual assimilation into the
strategic US war-fighting arsenal. In a letter to the chief chemical officer,
the US Air Force first stated the military requirements of an anticrop BW
munition in September 1947, and procurement action was initiated for
some 4,800 E73 500-pound cluster munitions in October 1950. This mu-
nition was based on a modified propaganda-leaflet bomb and was in-
tended for the dissemination of the causal agent of stem rust of wheat.