26 BULLETIN 16, U. S. DEPARTMENT OF AGRICULTURE. 
the only way to free a field from the pest is by absolutely clean fal- 
low cultivation for a year or two or by growing only immune crops 
for two or three years so as to starve them out.* 
The Granville wilt, first observed in the eighties of the past century, 
isa bacterial disease communicated through the soil. In the flue-cured 
district the infested area so far as known is largely confined to one 
soil type in the southern part of Granville County, N. C. This soil 
naturally produces a very fine type of wrapper tobacco. The disease 
is spreading quite rapidly locally and now occupies a considerable 
area in that section, embracing one of the very best bright-tobacco 
areas which we have. Once the soil is infected, no practical means 
have yet been devised for controlling the disease, and it is difficult 
to prevent it from gradually spreading to other adjoining areas. 
While the disease is confined to a comparatively restricted area, it is, 
nevertheless, a very ruinous one in that section. 
The mosaic disease, frequently spoken of as calico or “mottling,” 
probably is the most widespread of all the tobacco diseases. Until 
recently it has been quite generally supposed to be simply a mani- 
festation of malnutrition, caused by unfavorable growing condi- 
tions. It has long been known to be infectious, however. It can be 
spread, for example, by rubbing the leaves of a diseased plant and 
then likewise rubbing the leaves of healthy plants. Recent tests by 
Mr. H. A. Allard, of the Office of Tobacco and Plant-Nutrition 
Investigations, Bureau of Plant Industry, go to show that the dis- 
ease is a specific infection and in the absence of such infection can 
not arise from impaired nutrition. It has been discovered that cer- 
tain aphids or plant lice are largely responsible for the dissemina- 
tion of the disease. Other names, such as frenching, walloon, etc., 
are apphed to a group of diseases resembling true mosaic more or 
less. Such diseases as the so-called “sore-shin” and “rotten-stalk” 
are sporadic and occasional in their appearance, and are thought to be 
due primarily to some mechanical injury which may admit disease 
germs that attack the tissues locally. 
The occurrence of so-called “dead spots” here and there over a 
field, particularly in the Old Belt section, in which the plants, with- 
out apparent cause, fail to make any growth, is a phenomenon fre- 
quently observed, especially in a dry summer following a very wet 
spring. The soil of these spots generally appears to be in as pro- 
ductive a condition in all respects as other parts of the field. The 
roots of the plants show no apparent injuries of any kind or eyi- 
dences of disease. No fully satisfactory explanation of the cause or 
means of remedying the trouble are known to the writer. 
1For a full discussion of nematodes and methods of eradication, see “ Root-Knot 
and Its Control,” U. 8S. Department of Agriculture, Bureau of Plant Industry, Bulletin 
217, 1974; 
