TOBACCO INVESTIGATIONS. 23 



Tobacco Diseases. 

 In the Seed Bed. 



It may be stated on the authority of growers that while the weather 

 conditions in 1916 were unfavorable to a rapid and uniform development 

 of the seedlings, the beds were relatively free from parasitic diseases. 

 Comparatively little damping-off of seedlings was reported, but the chief 

 trouble seems to have been the checking of plants due to cool, moist 

 weather conditions early in the season. After setting in the field, recovery 

 was fairly rapid in most instances, and vigorous plants were produced. 

 Judging from field examinations later in the season there probably was 

 less "mosaic" in the seed beds than in some years past, as the number of 

 mosaicked plants on a large number of fields observed was less than what 

 is considered the normal infection. 



The practice of sterilizing the seed beds by means of steam or formalde- 

 hyde — preferably the former for the sake of convenience — is on the 

 increase, and with more attention being paid to such details as high 

 pressure, complete sterilization of all soil in the beds, etc., more uniformly 

 favorable results should be obtained. 



It is believed, however, that the practice of sterilization of the same 

 soil in seed beds year after year may not eventually produce the results 

 desired, as we really know very little as yet about the action of steam on 

 the soil, and its effects may prove detrimental if long continued. Thorough 

 sterilization, when necessary, is recommended rather than indiscriminate, 

 careless, or partial sterilization, which only adds to the expense of the crop. 



As to the presence of the root-rot fungus {Thielavia basicola Zopf.) in 

 the seed beds in 1916 no positive data are at hand, as our field work was 

 started too late to allow of any examination of the plants in the seed beds. 

 It is fallacious, in the case of root-rot, to draw conclusions from field obser- 

 vations as to its probable prevalence in the seed bed, owing to the fact that 

 the causal fungus is apparently well established in many of our fields, and 

 has been for some time. It becomes generally of great importance, from an 

 ecoyiomic viewpoint, only in certain years when favorable environmental con- 

 ditions for its development exist. Thorough sterilization of the seed bed 

 will also control this fungus when it occurs there. From data at hand it 

 is believed that many seed beds, heretofore unsuspected, are infected to a 

 certain degree with the root-rot fungus. 



In the Field. 



In order of importance and frequency of occurrence the diseases affecting 

 tobacco in Massachusetts may be classified as follows: Thielavia root-rot, 

 "mosaic" and allied diseases, leaf spots of various kinds, including "rusts," 

 damping-off in the seed bed, stem-canker, root-rots apparently induced by 

 Fusarium or closely related forms, root-rots apparently induced by 

 Rhizoctonia forms, albinism and similar chlorotic conditions, sun^scald of 



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