JOURNAL OF AGRIOJ1HJRAL RESEARCH 
Vol. XXI Washington, D. C., May 2, 1921 No. 3 
COTTON ROOTROT IN THE SAN ANTONIO ROTATIONS 
By C. S. Scofield, Agriculturist in Charge, Western Irrigation Agriculture, Bureau of 
1 Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The disease known as cotton rootrot has been prevalent on the San 
Antonio Experiment Farm since cotton experiments were begun there in 
1906. It was not, however, until 1912 that definite observations on the 
occurrence of the disease were made a matter of record. In that year 
counts were made of the number of cotton plants affected by rootrot in 
certain plots in a series of crop-rotation experiments, and the proportion 
of these diseased plants to the total number of plants in the plots was 
computed. Similar observations have been made each year since 1912, 
so that with the season just passed there are available eight years’ 
records of the disease in these rotation fields. 
In 1916 the disease was so serious that more detailed observations 
concerning it seemed justified, and at the close of that season each of 
the cotton plots in the rotation fields was carefully measured and a 
diagram was made, showing the spots in which the plants were dead 
from the effects of the disease. Each season since 1916 similar diagrams 
have been made of each cotton plot. 
It has been thought that the best remedy for cotton rootrot was to 
be sought through a . suitable rotation of crops, supplemented by deep 
plowing and thorough tillage. The rotation experiments here considered 
include a number of different crop sequences as well as some very different 
methods of tillage. While these rotation and tillage experiments were 
not planned with particular reference to rootrot control, they afford an 
opportunity to observe the reactions of the disease to different treat¬ 
ments during a series of years. 
During the eight years of record, 1912 to 1919, the disease has become 
increasingly serious in these rotation plots, as is shown in Table I, which 
gives for each year the average percentage of plants killed by rootrot 
in all the cotton plots in the rotation experiments. 1 There were 25 
1 The actual increase in severity of the disease has been somewhat less than the data here given would 
indicate, for the reason that prior to 1916 the rootrot counts were made before the end of the growing season. 
The actual dates on which the counts were made are as follows: 1912, Aug. 13; 1913, Sept. 4; 1914, early 
September (exact date not recorded); 1915, Sept. 28; 1916, Oct. 23 to 25; i 9 i 7 > Oct. 25 ;.j9i 8, Oct. 23 to 29; 
1919, Oct. 27 to 31. 
Journal of Agricultural Research, 
Washington, D. C. 
xl 
(“ 7 ) 
Vol. XXI. No. 3 
May 2,1921 
Key No. G-224 
