May a, 1921 
Cotton Rootrot in the San Antonio Rotations 
125 
are of the same sort that in the shorter rotations were found to be without 
effect on the extent of rootrot injury. Thus, rotation B~4a, which shows a 
mean annual loss of only 0.6 per cent, differs from rotation B-4b with a 
annual loss of 6.9 per cent only in having a year of Sudan grass instead of 
oats followed by field peas. Likewise, in the four-year rotation one of 
these, A-4L with an annual loss of 0.4 per cent, differs from the other, 
having an annual loss of 15.0 per cent, only in that the field peas are cut 
for hay instead of being plowed under. These differences of treatment 
can hardly be regarded as sufficient to account for the striking differences 
in the extent of rootrot injury. 
Having in view the whole of the results from these rotation experiments, 
one is forced to the conclusion that the control of rootrot is not to be found 
through any ordinary system of crop rotation or of tillage methods. 
Table IV. —Percentage of plants killed by rootrot in the various three-year and four-year 
rotations at the San Antonio Experiment Farm, 1912-1919 
THREE-YEAR rotation 
<* No record. 
