26 MASS. EXPERIMENT STATION BULLETIN 195. 



ated. The second class is by far the more prevalent, and only in rare 

 cases during 1916 were organisms found associated with a leaf spot. The 

 amount of damage caused by leaf spots of this character is apparently 

 slight, judging from the data at hand, but it is possible that more extended 

 examination of fields may show different results. 



The leaf spots not due to organisms were rather numerous in 1916, 

 especially those classed as "rusts" by growers. One type of these "rusts" 

 is usually found associated with the mosaic disease, and here the rusted 

 spots which are made up of dead tissue are rather large and often coales- 

 cent, so that a comparatively large leaf area may be affected. Another 

 type of "rust," believed by the writer to be associated also with the later 

 stages of mosaic, was observed. In this case the spots were small, more 

 regular in outline, not coalescent, and more thickly distributed over the 

 leaf. There is some question, however, whether this type is always associ- 

 ated with the mosaic disease, as the same condition has been observed oc- 

 casionally on plants not affected with this disease. In some shade-grown 

 areas another type of spot or "rust" was observed, and it was not associ- 

 ated with mosaic. Here the spots were small, regular in outline, and widely 

 scattered, some of the leaves showing only one or two such spots. It is 

 not certainly known what the cause of this type of spot is, but it resembles 

 a spot found in other tobacco sections where a lack of potash is said to 

 exist. It may be due to other causes, however, and it is useless to even 

 hazard an opinion on the question at this time. The whole matter of 

 leaf spots requires investigation, particularly those spots which are not 

 caused by organisms. It is expected that a study of these troubles will 

 be taken up at a later date. 



Mosaic disease was present in 1916 on many fields, but from an estimate 

 of the amount on fifty-one areas it was apparently not present to so large 

 an extent as in some j^ears, approximately less than 3 per cent of the 

 plants havirrg the disease on commercial leaves. No account w^as taken 

 of plants contracting the disease on the sucker growth appearing after 

 topping, as it is believed that the presence of the disease on such growths 

 does not affect the commercial leaves. The percentage of infection, in 

 general, that season (1916) was below what may be considered the normal 

 infection. (This count, however, included three very badly infected 

 fields where a large percentage of the crop was affected, and this raised the 

 percentage of infection considerably.) The prevalence of mosaic disease 

 seems to be less than it was some years ago, and there has been only rela- 

 tively small damage from this trouble in the tobacco section, as a whole, 

 in the past two or three years. If more attention is paid to careful handling 

 of plants in removal from the seed bed and during transplanting, the 

 damage resulting from this disease can be reduced to an almost negligible 

 amount. More attention should also be paid to fitting the land and keep- 

 ing it in the best condition during the transplanting time and until the 

 plant has obtained a good start. There is no question but that proper 

 attention to such details and to the rejection of diseased plants in the seed 



