Proceedin(;s of Seventeenth Formal Institute 2o9 



Leaf roll and curly dwarf are transmitted through the seed 

 and, as with mosaic, affected tuhers can not be detected ; in 

 growing plants these diseases may be detected quite readily. 

 Fields showing more than 10 per cent of either of these diseases 

 at the beginning should be disqualified for seed. Fields showing 

 less than 10 per cent may be accepted after thorough roguing. 



The same rule should apply to fields containing many small, 

 weak plants unaflected by any recognizable disease. The presence 

 of a high percentage of small, weak plants is evidence that the 

 strain is degenerating, and it is unsafe to use for seed even 

 tubers from the large plants in such fields. 



Similar limits should be j^laced upon blackleg. The presence 

 of over 10 per cent of blackleg should disqualify a field. If 

 there is less than 10 per cent the field may be accepted after 

 thorough roguing. It should bo borne in mind that the corrosive 

 sublimate treatment of seed tubers is a preventive of blackleg. 



The wilt diseases (Fusarium and V erticillium) and the stem- 

 end browning of tubers require stricter treatment. These dis- 

 eases are especially dangerous because they are transmitted 

 through the seed, and there is no known method of efiicient pre- 

 ventive seed treatment or of eradicating them when once estab- 

 lished. Fields showing, previous to roguing, over 2 per cent of 

 plants affected with wilt should be disqualified ; and not to exceed 

 1 per cent of tubers affected with distinct stem-end browming 

 should be pennitted at the final inspection. 



other considerations 



In addition to the above there should be some regulation re- 

 garding the size or weight of tubers. For late varieties I should 

 recommend two to twelve ounces, and for early varieties two to ten 

 ounces as being the proper limits of weight. Also, it should be 

 stipulated that, in fields acceptable for seed, good cultural con- 

 ditions shall prevail and that the yield shall be a satisfactory 

 one for the variety. 



The discussions at the several conferences which have been held 

 over this matter show that it will be very difficult to reach close 

 agreement on seed potato standards until after there has been more 

 experience with the actual work of inspection and certification. 



