reduces the yield and market value of the crop. 
Less severe but important losses result also from fungus and 
bacterial wilts and tuber rots. The most important fungus diseases 
are verticillium wilt, fusarium wilt, and the rhizoctonia disease. 
The bacterial diseases are blackleg and ring rot. Most of these 
diseases may occur wherever potatoes are grown, but they are parti- 
cularly prevalent in the North Atlantic, North Central, and Pacific 
coast regions. 
Virus diseases rank with late blight, early blight, and scab as 
a cause of losses in potatoes. Since the viruses are carried in 
seed tubers, they occur wherever potatoes are grown. Losses result 
from decreased yield and quality of tubers and increased cost of 
production due to the necessity of using certified seed that is so 
grown as to keep the plants comparatively free from infection. The 
more important virus diseases are the mosaic diseases, leaf roll, 
spindle tuber, yellow dwarf, and purple top. 
Both late and early blight can be controlled fairly well by fre- 
quent applications of fungicides. Some varieties resistant to late 
blight are available. Scab losses can be reduced by use of clean 
seed, chemical seed treatment, and crop rotation. Tolerant varieties 
are available. Losses from wilts and tuber rots can be reduced by 
use of certified seed and crop rotation. Serious virus disease 
losses can be avoided by use of certified seed. Varieties resistant 
te certain viruses have been introduced. 
The root-knot and meadow nematodes cause minor loss in yield and 
quality of tubers. Rotation helps to reduce damage. 
Another nematode that is of great potential importance is the 
potato golden nematode, which occurs in this country only in a 
restricted area on Long Island, New York. This nematode attacks the 
roots, weakening and stunting the plants and consequently greatly 
reducing tuber yield. Loss estimates for it-are not included in the 
tables because potato production on infested land is prohibited, but 
. its destructiveness is shown by experience in Europe and on Long 
Island. It lives for years in the soil even in the absence of host 
plants; on badly infested land profitable potato crops can ‘be pro= 
duced only once in 5 to 8 years, and no method of eradicating it is 
known. Losses in heavily infested fields range from one-third up 
to almost three-quarters of the yield. The strictest possible 
measures to prevent further introduction and spread in this country 
are being enforced by Federal and State governments. 
Shallots 
The shallot crop is damaged by the same diseases that attack onions. 
Much of the loss is caused by pink root, downy mildew, purple blotch, 
@-hJ- 
