UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 765 & 
Contribution from the Bureau of Plant Industry a 
WM. A. TAYLOR, Chief 
Washington, D. C. Vv April 18, 1919 
STRAINS OF WHITE BURLEY TOBACCO RESISTANT 
TO ROOT-ROT. 
By JAMES JOHNSON, Agent, and R. H. Mitton, .Assistant, Office of Tobacco 
Investigations. 
CONTENTS. 
Page. Page. 
Relation of root-rot to the cropping system in Development of Burley strains resistant to 
practicaltobacco culture. .... Be oe eee 1 TOOE-TOGH Ee emeeree metciele sees eine Secs eae eros U 
Description of root-rot........-.---.--------- 2 | Experimentsin the White Burley district of 
PanNssonvHe GIsease...-2-.------2-22e.s---2-- 5 Keentucksy Sarnia eas o/s oa ee Nee ee 8 
Varietal resistance and susceptibility --.-.--- 5 | Resistant Burley strains recommended for 
sick soils in White Burley districts......... 10 
RELATION OF ROOT-ROT TO THE CROPPING SYSTEM IN 
PRACTICAL TOBACCO CULTURE. 
In the systems of tobacco culture prevailing in the United States 
there are two outstanding extremes in the management of the land. 
In one case tobacco is grown on the same soil year after year for 
indefinite periods, while in the other there is a rotation of crops in 
which only one or two crops of tobacco are grown on the land in a 
period of 8 to 10 years. The continuous-culture system is character- 
istic of the cigar-tobacco section of New England and to a con- 
siderable extent of Wisconsin and Ohio, while on the tobacco lands 
of Pennsylvania the systematic rotation of crops is the rule. In 
the southern tobacco-growing sections generally there is consider- 
able variation in farm practice in this particular, but in most dis- 
tricts it is seldom that the system of continuous tobacco culture is 
attempted. The practice of growing only one or two crops of tobacco 
on the land and then allowing a period of 6 to 10 years to elapse be- 
fore cropping to tobacco again is especially characteristic of the 
Burley section of Kentucky and the adjoining States. 
These radically different practices have not developed without 
good reason on the part of the growers, and the cause is a matter 
96766°—19—Bull. 765 
