WHITE.BURLEY TOBACCO RESISTANT TO ROOT-ROT. a 
haps, have noticed in certain years or on some plants roots which are 
not only small in size and number but which are decayed and brown 
or black, instead of having normally abundant roots of pure-white 
color. No great attention is given to this, since it is known that such 
plants when set in the field send out new roots and may appear to 
start out almost as well as healthy plants. Nevertheiess, this condi- 
tion is frequently the source of future difficulties. The plants may 
or may not recover from this trouble, depending on a number of 
environmental factors. Fortunately, plants so affected often do not 
make a sufficiently vigorous growth in the beds to permit transplant- 
ing; hence they save some discouragement later. In passing, then, it 
may be said that the root dieenee. is one of the common. causes of 
plants turning yellow and failing to grow properly in the beds. 
It has been found that the amount of damage done by the root 
disease is largely dependent upon the temperature of the soil, which 
is, of course, controlled largely by the temperature of the air. Low 
temperatures (60° to 75° F.) favor root-rot, while high soil tem- 
peratures (80° to 100° F.) practically prevent the disease from de- 
veloping. Therefore, if the season is relatively warm, diseased plants 
may partially or wholly recover. However, all growing seasons have 
periods, sometimes extending over most of the season, when the 
weather is cool. Recovery then does not occur or is very slow. The 
plants refuse to grow, or make little headway as compared with 
neighboring fields on ground free from disease, and the crop pros- 
pects are much reduced. Frequently, however, after long cool 
periods a week or two of very warm weather starts the crop into a 
very rapid growth if sufficient moisture is present or if plenty of 
rainfall occurs. 
A common occurrence, even in the Burley district, where a rota- 
tion system is practiced, is the transplanting of ineall ary (or diseased ) 
plants into soils which already harbor the root trouble. These soils 
we will hereafter cail “sick” soils. The result so far as crop pro- 
duction is concerned will depend largely on seasonal conditions, espe- 
cially as to soil temperature, as previously described. A crop may or 
may not be produced. The situation as a whole, however, is much 
more serious, since this is by far the most common way in which the 
disease starts, and all the plants become involved. For all practical 
purposes it is safe to say that in the Burley district substantially all 
fields which have grown two or more crops of tobacco (and often 
those growing only one crop) are more or less “tobacco sick.” This 
disease does not attack grains, corn, or hemp, and, in fact, affects no 
other agricultural crop except certain legumes, ieee sick tobacco 
soils being capable of growing such crops in a Raneractory manner 
80 far as root-rot is concerned. 
