INSECTS AND DISEASES 97 



appears to be, on new ground, never less than five 

 years. 



It appears to be during the germination and 

 earliest growth of the onion seed only that the fungus 

 threads, developed from the spores, make their en- 

 trance into the onion seedling. Onions grown in 

 warm, light soils are usually more likely to be smutted 

 than if they are grown in heavy, wet land. 

 It seems undoubtedly true that the yellow and espe- 

 cially the red varieties are less susceptible than the 

 white to this, as to most other diseases affecting 

 the crop. 



Dissemination The popular impression that smut 

 is disseminated principally in the planted seed is one 

 which is quite erroneous. As a matter of fact seed 

 onions are not attacked by smut, and the presence of 

 smut spores in the seed is not to be considered for a 

 moment as a cause of its dissemination. It is very 

 probable, however, that smut may in some instances 

 be carried on seeds grown in smutted districts, the 

 spores adhering to their surface as any small particles 

 of dust might do. Any course of procedure in har- 

 vesting or in preparing seed which involved the dust- 

 ing of even a small amount of smutted earth upon 

 it, would render the seed dangerous for this reason. 

 Proper care in gathering and handling seed should, 

 however, obviate this danger entirely. 



The local dissemination of smut is due to four 

 principal causes. First, through agricultural imple- 

 ments, plows, harrows, weeders, rakes, etc, which 

 spread the soil containing smut spores, both by scatter- 

 ing the surface earth over a smutted field and, unless 

 they are thoroughly cleaned, by carrying earth con- 

 taining smut spores into fields subsequently worked 

 upon. Secondly, through the adherence of the same 

 smutted earth to the feet of men and farm animals 



