THE EOOT-ROT OF THE SWEET POTATO 
By L . L. Harter, 
Pathologist , Cotton and Truck Disease and Sugar-Plant Investigations , 
Bureau of Plant Industry 
INTRODUCTION 
On August 9, 1912, Mr. O. H. Weiss sent the writer some diseased 
sweet-potato (Ipomoea batatas) vines from the vicinity of the Dismal 
Swamp, Va., with a request for information regarding the nature of the 
trouble. The stems for a short distance above the ground were covered 
with black fruiting bodies of a fungus, and suggested macroscopically 
the conidial stage of Diaporthe batatatis , the cause of the sweet-potato 
dry-rot. Careful examination of the material showed that in structure 
these fruiting bodies differed from those of the dry-rot organism, although 
it was apparent that both fungi belonged to the same general group. 
The organism was isolated in pure cultures from material taken from 
diseased sweet-potato stems and its parasitic habits and growth in arti¬ 
ficial cultures compared with the dry-rot organism. 
On August 22, 1912, the writer visited the sweet-potato fields near the 
Dismal Swamp in order to observe the disease under natural conditions 
and to ascertain the extent of the loss. The disease was found in prac¬ 
tically every field, causing a loss of from 10 to 50 per cent of the crop, 
and in exceptional cases even more. 
During August, 1913, the disease was found for the first time in many 
fields near Cape Charles and Keller, Va. Whether this is the first appear¬ 
ance of the disease in this part of the State is not known. The writer 
had inspected many fields in this section for several summers previous to 
1913 and never observed the disease. It seems likely, therefore, that the 
disease is either new to these places or has heretofore occurred only to 
a very limited extent. The organism was isolated from specimens col¬ 
lected at both Cape Charles and Keller, and it was found to be identical 
with the one obtained during 1912 and 1913 from the vicinity of the 
Dismal Swamp. 
Inquiry among the farmers in the vicinity failed to give a definite idea 
as to how long the disease has been prevalent. It was learned, however, 
that the disease has increased in severity in the last few years, and if not 
checked is likely to prove a serious handicap to the growing of a crop 
that would otherwise be a profitable industry. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
(231) 
Vol. 1, No. 3 
Dec. io, 1913 
G—7 
