8 CIRCULAR 692, U. S. DEPARTMENT OF AGRICULTURE 
Tobacco grown after tobacco was killed by the disease early in the season, and 
the crop was a complete loss (fig. 2, A). The rotation of native weeds gave only 
slight reduction in wilt severity, but this was expected, as several species of wilt- 
susceptible weeds were abundant in the fallow. Tobacco grown after 3 years of 
crabgrass and sweetpotato was also badly diseased. During 1937 and 1938, how- 
ever, tobacco grown after 1 or 2 years of crabgrass and sweetpotato was not so 
severely damaged as in 1939, showing that these two rotations varied widely in 
effectiveness during different seasons. Rotations of redtop and corn (fig. 2, B) 
were the most effective, as shown by the lowest percentages of wilted plants and 
the highest yields, evaluated by 1939 prices at more than $120 an acre (see table 2, 
last column). Corn was more effective than other crops in 1937, 1938, and 1939. 
Fictre 2.—-Control of bacterial wilt by rotation on large plots: A, Planted in 
tobacco continuously since 1935; B, tobacco growing after 3 years of corn, 
Photographed July 20, 1939. 
