POTATO DISEASES IN I907. 313 



In commenting upon the fact that none of the treatments 

 entirely eliminated scab from the crop it should be remembered 

 that even the smooth seed had some scab spots, and no treat- 

 ment has yet been devised which will penetrate the tissues of 

 the potatoes in these spots, kill all the scab germs, and not 

 endanger the germinating qualities of the seed. However, if 

 by treating very scabby seed, the amount of scab in the result- 

 ing crop is reduced to 1 per cent or less, it seems reasonable 

 to assume that by using only smooth seed and treating it to 

 kill any germs which may be on the surface the infection of 

 clean ground may be avoided, and probably the danger of 

 increasing the disease on ground already infected will be less- 

 ened. 



The fact that so little scab developed from the untreated seed 

 detracts somewhat from the value of the results, although a 

 glance at the table shows that in every case the treatment 

 materially reduced the per cent of scab in the resulting crop. 

 However, only 6.5 per cent of scab in a crop from very scabby 

 seed is unusual. For 4 consecutive years the writer found the 

 per cent of scab in a crop from very scabby seed like that in 

 question varied from 19.8 per cent to 63 per cent.* Moreover 

 smooth seed invariably produced less scab than scabby seed 

 and treated seed less than untreated seed. It is of interest in 

 this connection to call attention to the fact already stated that 

 scab in general was very much less prevalent than in the pre- 

 ceding season, although that of 1906 was much the dryer of 

 the two. 



It is also of interest to note that sodium benzoate materially 

 reduced the amount of scab in the resulting crop. However, 

 with the present prices quoted for this chemical its use cannot 

 be recommended as a substitute for formalin or corrosive sub- 

 limate, the materials commonly used in treating the seed by 

 soaking. 



The results from gas disinfection were perfectly satisfactory 

 on the portion of the field where comparatively clean, treated 

 seed was used on clean land. A crop free from scab resulted 

 and it is believed the introduction of scab germs into this soil 



* Vt. Sta. Repts. 15, p. 229 (1902) ; 16. p. 167 (1903) ; 17, p. 400 (1904) ; 

 and 18, p. 289 (1905). 



