4 THE DANGER OF USING FOREIGN POTATOES FOR SEED. 



TWO SERIOUS DISEASES. 



The most dreaded of these is the wart disease, concerning which 

 so much has been written in England and in this country. Potato 

 wart, or " black-scab," is a disease of the tubers which forms large, 

 irregular excrescences, at first greenish or white and later black. 

 These begin near the eyes, but in advanced cases involve the whole 

 tuber, which is converted into an unrecognizable and useless mass. 

 There are no conspicuous evidences of this malady in the foliage of 

 affected plants. The more severe cases exhibit the disease at the 

 surface of the ground, where the worst affected tubers protrude 

 above the soil. Other tubers have small warts, but are usable for 

 culinary purposes, and some may be so slightly affected as to pass 

 as healthy. It is a disease difficult to detect by inspection in its 

 early stages, and there is nothing to prevent its distribution in the 

 United States on imported potatoes. This danger is the greater 

 since the badly infected districts of England lie near Liverpool, 

 from whence many shipments are made. This disease has been 

 jTiore fully described in two publications of the Department of 

 Agriculture, Circular No. 52 of the Bureau of Plant Industry and 

 Farmers' Bulletin 489, both of which may be had free of charge 

 upon application to the Secretary of Agriculture or to a Senator. 

 Representative, or Delegate in Congress. 



Such dangers as the present emphasize the need for a national 

 quarantine law to enable the Secretary of Agriculture to exclude 

 diseased or insect-infested plant products or imports from localities 

 known to have these pests. Such a bill has been pending before Con- 

 gress for several years, but as yet no action has been taken. 



The potato wart is not the only disease likely to be imported. 

 There is another tuber trouble, known as Spongospora scab {Spon- 

 gospora subterranea (Wallroth) Johns.), which would be an unde- 

 sirable addition to our already long list of diseases brought from 

 foreign sources. This scab causes small spots or even tumor-like 

 groAvths of small size. It does not destroy the potato, as may the 

 wart, but lessens its market value. Spongospora scab is quite preva- 

 lent in Ireland. Large quantities of ^wtatoes are now being imported 

 from that island. 



A third trouble which may be introduced on imported potatoes is 

 the black-leg, a bacterial disease which can rarely be detected in the 

 tubers, as the infection is always internal. It manifests itself in the 

 field after the potatoes are half grown. The tops yellow and curl 

 up, the stem blackens and. decays at the base, and the hill dies. This 

 disease has already been introduced into many of our States, i^rob- 

 ably from England by way of Canada. The danger is no less in 



[Cir. 93] 



