4 FARMERS BULLETIN 996. 



bed- and tlit? eliief object of burning has been to free the bed from 

 weed seeds. 



In- jth,e licrthei-n districts permanent seed beds with glass covers 

 are in more or less general use, and the widespread appearance of 

 fungous diseases, especially root-rot, has made some sort of steriliza- 

 tion necessary. Since open fires are impracticable in these districts 

 a process of steam sterilization has been worked out, which now is 

 used extensively in the cigar-leaf producing districts of the Connec- 

 ticut Valley, Pennsylvania, and Wisconsin and has been employed 

 with success in several other sections, notably in western Kentucky 

 and Tennessee and in the Burley district. This method is both eco- 

 nomical and effective, and with more or less modification is adapted 

 to practically all tobacco-growing districts. 



ROOT-ROT IN THE SEED BED. 



Within recent years the discovery of the prevalence of a root-rot in 

 the seed bed and in the field has brought about a wide demand for a 

 suitable method of control. The fungus 1 which causes this root-rot is 

 so small that it can be seen only with the aid of the microscope. It may 

 attack the plant at any time after the germination of the seed, and 

 usually can be recognized easily by its effect upon the roots. In the 

 earlier stages brown or black spots appear on the roots. These vary 

 in size from small dots to areas that may extend along the taproot 

 and laterals for an inch or more. In these diseased portions spores, 

 or reproductive bodies of the fungus, may be found by examination 

 with the microscope. As the fungus attacks the roots the diseased 

 parts become successively brown and black, and the root tissues die 

 and fall away, seriously affecting the vitality of the plant. 



The fungus lives in the soil from year to year; hence, a bed once 

 infested should not be used again until the disease has been elimi- 

 nated. New seed beds may be infected by stable manure or decayed 

 leaves used for fertilizing, or by wind-blown vegetable matter carry- 

 ing spores of the fungus. Seedlings seriously attacked by root-rot 

 are not fit for transplanting, and, furthermore, they may be the 

 means of establishing the disease in the field. It is especially im- 

 portant, therefore, that the disease be eliminated from the seed bed. 

 An effective and economical method of control of the root-rot in the 

 seed bed is found in the sterilization of the seed-bed soil. 



OLD METHOD OF STERILIZING TOBACCO SEED BEDS. 



For many years before the adoption of sterilization with steam, 

 open fires on the soil had been used. The open-fire method came into 

 use chiefly because of its value in freeing from weed seeds the spot 



1 The technical name of this fungus is Thielavia basicola. 



