4 WABT DISEASE OF THE POTATO. 



and remains of the cell walls of the potato, is broken up, the spores 

 are liberated in millions, and the land is badly infected for years." 

 (Giissow, 1909.) (See Pis. I and II.j 



In a mild attack the eyes first appear grayish, then turn brown, and 

 finally black, while in a healthy tuber these are whitish or purplish in 

 color. The tuber is onl}^ slightly disfigured and its keeping qualities 

 do not seem to be impaired. 



While the tuber is the part of the plant chiefly affected, infection 

 may take place in all the young tissues of the plant, the roots, stolons, 

 stems, and even the leaves. 



THREATENING NATURE OF THE DISEASE. 



All reports indicate that the potato wart is one of the most serious 

 of all known diseases of the potato. It converts the tuber into an 

 ugl}', irregular, and utterh' unsalable growth. When established in 

 a fleld it ma}^ affect the entire crop, and the land remains so infected 

 that potatoes can not be successfully grown for six or more years. 



We quote from writers abroad the following: 



J. W. Eastham (Yearbook, College of Agriculture and Horticulture, 

 Holmes Chapel, 1904): "When once established in the land it is use- 

 less to grow potatoes again until the pest has been starved out or 

 otherwise destroyed; but so far as is known no other crops are liable 

 to be attacked. Quite the worst case seen in Cheshire ocxjurred on 

 land that had not borne potatoes for six years; 'seed' from the same 

 source as that employed on this land yielded satisfactory results else- 

 where, indicating that spores were not introduced by the seed, whilst 

 the manure emplo3'ed started no infection elsewhere. This indicates 

 prolonged vitality on the part of the fungus, which would render 

 starving out a very tedious process." 



E. S. Salmon (Gardeners' Chronicle, 1907): "It is quite clear, 

 however, that the 'black scab' disease threatens to inflict such serious 

 injur}^ on the potato crop as to warrant the Board of Agriculture 

 taking official action. * * •• The disease is viewed with alarm by 

 both the scientific and the practical man, and yet no steps are being 

 taken to deal with this pest which, if it is allowed to spread through 

 the country and to reach Ireland, will cause losses of hundreds of 

 thousands of pounds.'' 



Borthwick (1907), referring to an outbreak in Scotland, says: "The 

 whole crop was damaged to the extent that the}' could not be used. 

 They were quite useless, the earl}^ varieties being, if anything, worse 

 than the late, especially the early kidneys. The disease was first 

 noticed when the new potatoes began to form. It first appeared on 

 the stems as a greenish -looking canker, which attacked the tubers as 

 they grew and soon made them a mass of corruption." 



[Cir. 52] 



