4 BULLETIN 1256, U. S. DEPARTMENT OF AGRICULTURE. 



careful study of some diseases in certain sections at one time or 

 another furnishes some basis, however, for the conclusion that the 

 average annual loss amounts to many millions of dollars. The 

 losses from root rots in certain years certainly exceed $10,000,000. 

 Some of the recent wild-fire and black-fire epidemics have alone 

 caused losses to the extent of millions of dollars in certain districts. 

 Other leaf-spot diseases and mosaic are always present to a consid- 

 erable extent in one section or another and materially reduce both 

 yield and quality. The damages during curing and fermentation 

 alone run into hundreds of thousands of dollars annually. If we 

 estimate the average annual loss from tobacco diseases in the United 

 States at 5 per cent of the crop value, which is believed to be a very 

 conservative figure, the loss based on the present value of the crop 

 would be close to $25,000,000 per year. 



THE PLANT BED AS A SOURCE OF INFECTION. 



A very considerable number of diseases which cause great damage 

 in the field have their origin in the plant bed. Preventive measures 

 should, therefore, be used in the preparation of the seed beds to 

 assure success in controlling the diseases in question. The most 

 common seecl-bed disease is known as damping-off or bed-rot and 

 may be caused by several different fungi. The parasites of this 

 class are, however, ordinarily important only in the seed beds, 

 although they may occasionally carry over into the field as black- 

 leg, canker, or sore-shin. 



In the case of black root-rot the most serious injury follows trans- 

 planting to infested soils, although frequently much injury results 

 from the occurrence of this disease in plant beds and the subsequent 

 transplanting of infected plants to disease-free soils. 



The mosaic disease of tobacco, which is very rarely noted or re- 

 garded as of any importance in the plant beds, usually originates, 

 however, in the seed beds, and its presence there is largely respon- 

 sible for the general field infections frequently observed in many 

 sections. 



Recently it has been shown that several bacterial diseases, i. e.. 

 wild-fire, black-fire, and Wisconsin leaf -spot, some of which are very 

 important in the districts where they occur, are in practically all 

 cases traceable to plant -bed infection. Many other diseases of tobacco 

 may also make their first appearance in the seed bed. 



The production of plants for transplanting entirely free from 

 such diseases as mosaic, wild-fire, and black-fire is therefore highly 

 important, since at no other point can the prevention of these 

 diseases be accomplished more efficiently or economically. 



The principles of control are essentially similar for all the diseases 

 concerned, that is, eliminating the chances of the introduction to the 

 seed bed of the parasites concerned in these diseases or destroying 

 them if already present. The measures which can be applied can be 

 included under the general term " sanitation.'' 



PLANT-BED SANITATION. 



The following summary of sanitary measures which should be ap- 

 plied in seed-bed preparation, particularly on farms where mosaic 



