238 Report of Farmers' Institutes 



sorted out. I think that the claim, sometimes made by southern 

 growers, that seed from blighted fields is especially liable to rot 

 after planting, and gives pooi stands, is not well founded. Rotting 

 of the seed pieces after planting is usually due to other causes. 

 With reasonable care in sorting the seed at planting time very 

 few blighted tubers need be planted. Neither is there any great 

 danger of starting blight through the use of seed from blighted 

 fields. While outbreaks of blight have sometimes been traced 

 to the use of blighted seed, such cases are rare, and experience goes 

 to show that fields planted with blight-free seed usually blight as 

 early and as severely as those planted with seed from unblighted 

 fields. Blight-free seed has not the advantages often claimed for 

 it ; yet potatoes from fields showing much rot can hardly qualify 

 as first-class seed. 



Mosaic is a new disease which promises to become a very im- 

 portant factor in the seed potato business in this state. It is 

 transmitted through the seed, yet shows no evidence of its presence 

 in the tubers. There is no means by which affected tubers may 

 be detected. Badly diseased plants are easily detected by their 

 wrinkled, curled foliage and small size; but in mild cases it is 

 often difficult to distinguish diseased plants from healthy ones. 

 This fact makes inspection for mosaic difficult and uncertain. 

 As yet it is uncertain how strict it will be necessary to be in re- 

 gard to mosaic. With some varieties it is very destructive, and 

 recent experiments at the Geneva Station indicate that, under 

 some conditions at least, tubers from slightly affected plants 

 may j^i'oduce plants which are entirely worthless. Thus, accord- 

 ing to present indications, fields showing much mosaic are to 

 be avoided as a source of seed. However, we are confronted 

 by the fact that mosaic is widespread throughout Maine and 

 northern Xew York; and, if we are to have enough seed potatoes 

 to supply the demand, we shall be obliged to pass fields contain- 

 ing some mosaic. In view of this, and the difficulty of detecting 

 mild cases of the disease, it is suggested that, for the present, the 

 limit on the amount of mosaic peiinissible be placed at 5 per 

 cent. ISTo field showing over 15 per cent of mosaic should be 

 passed even though the owner is willing to rogue it, and fields con- 

 taining a smaller amount than 15 per cent should be rogued 

 down to 5 per cent or less before being accepted. 



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