GAS TREATMENT FOR THE CONTROL OF |) 
BLUE MOLD DISEASE OF TOBACCO | 
By Epwarp E. Cuayton, senior pathologist; JoHn G. GAINES, assistant pathologist; | 
“KENDALL J. SHAW, agent; THomas E. Smiru, agent; and THomas W. GRanaM, | 
agent, Division of Tobacco Investigations, Bureau of Plant Industry | 
United States Department of Agriculture, Bureau of Plant Industry, in cooperation with | 
the Georgia Coastal Plain Experimental Station, the North Carolina Department of | 
Agriculture, and the Agricultural Experiment Stations of North Carolina, South 
Carolina, and Maryland 
Blue mold is a constant expense and threat to tobacco growers, | 
particularly in the Southeastern States. It is always hable to cause © 
transplanting delays or actual plant shortage. Most serious damage — 
has occurred in Georgia, where 80 percent of the plants were killed | 
in 1937, 25 percent in 1938, and 50 percent in 1939. Although blue 
mold occurs every year in practically every plant bed from Florida 
to Maryland and total losses are large, individual growers have a 
good chance of escaping severe damage, even in an area such as 
Georgia. As a result, there is a tendency for them to merely sow 
more beds rather than to go to the bother of undertaking control 
measures. However, the cost of blue mold is no small item. Thus, 
throughout the flue-cured region, plant-bed areas have been doubled 
because of blue mold, and this alone means an added expense of about 
$5,000,000 annually. Several reasonably effective blue mold control 
treatments are now available: (1) The benzol gas treatment, developed 
in Australia, which is safe and effective but is generally regarded 
in this country as too costly and cumbersome to be practical; (2) the 
copper oxide-cottonseed oil spray, reported in 1938, and (8) the para- 
dichlorbenzene gas treatment, a preliminary announcement of which 
was published by the authors in 1938 and which also has been reported 
upon subsequently by others. 
The spray treatment has the advantage of being inexpensive, and 
it also has an excellent physiological effect on plants that are to be 
transplanted. Spray treatment, however, must be started in advance 
of disease development, whereas gas treatment need not be started 
until after the disease is actually present in the bed. Theoretically, 
it is possible to completely eliminate blue mold from a bed by gas 
treatment, but practically it is doubtful whether this is ever done 
under actual plant-bed conditions. Numerous comparisons have 
been made of the spray and gas treatment, and in all these experi- 
ments satisfactory blue mold control was obtained with both. There 
were no measurable differences in the number of plants produced per 
unit area of bed, the earliness of the plants, or the field stands. It is 
concluded, consequently, that either the spray or the gas treatment, 
properly used, can be depended on to give adequate control of blue 
mold. It is the purpose of this leaflet to outline the simplest, most 
effective, and safest method of gas treatment, as determined by 
extensive tests conducted during the past several years. 
Gas Treatment With Benzol 
As has been mentioned, most growers in this country seem to regard 
the benzol method as impractical. One of the chief reasons appears 
276380°—41 Issued January 1941 
2 
Pernt ries 
