WHITE BURLEY TOBACCO RESISTANT TO ROOT-ROT. S 



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, inst'ead 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. Nevertheless, 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 disease 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 healthy (or diseased) 

 plants into soils which already harbor the root trouble. These soils 

 we will hereafter call "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, these sick tobacco 

 soils being capable of growing such crops in a satisfactory manner 

 so far as root-rot is concerned. 



