19-21.] 



The Control of Onion Smut. 



443 



EXPERIMENTS ON THE CONTROL 

 OF ONION SMUT, 



T. Whitehead, A.li.C.Sc, 

 University College of North Wales, Bangor. 



The attention of gro\Yers in this country was first drawn to 

 the new and serious disease of Onions and Leeks, called Sm.it, 

 by A. D. Cotton in this Journal in 1919.'*" The disease 

 which is due to the fungus Urocystis cepu.hc, and fortunately 

 appears to be localised in a few centres ; and there is no evidence 

 that it is spreading rapidly, if at all. It should be remembered, 

 however, that Onion Smut is a seedhng disease, and is very 

 easily overlooked at that stage in the growth of the plant when it 

 is most destructive, i.e., when it is in the two-leaf condition. Jt is 

 possible, therefore, that the disease is more widely distributed 

 than is at present suspected. 



The serious result that would follow any increased distnbutioii 

 of the disease is evident from the fact that in Northumberland, 

 where the most severe attacks have been experienced, a loss of 

 90 per cent, of the crop may be expected if the growing season 

 is unfavourable. 



As early as 1884, Worthington G. Smith!" expressed the fear 

 that Onion Smut was already present in this country. He was led 

 to this conclusion by the many complaints that onions were falling 

 into a black, dusty mass after harvesting. . It is not possible to 

 say whether the disease did exist at that time in this country, 

 but the fear expressed, at any rate upon the evidence given, 

 Wiis unfounded, for it is now kno^^Tl that Onion Smut does not 

 produce the symptoms described. There can be little doubt, 

 however, that the disease existed in this country many years 

 before it was first identified, in 1914, by W. B. Mercer, then 

 Adviser in Agricultural Botany at Armstrong College, Newcastle- 

 on-Tyne. 



The Northumberland Outbreak.— The eariy historv of the 

 two infected centre's in Northumberland has been investigated by 

 the writer. The disease was apparentlv first noticed in or about 

 the year 1900. In one case it appeared the first season after 

 purchasing seed from the south of England. Before this seed 

 had always been purchased from a small grower in Edinbui'gh, 

 and in view of the discovery in 1912 that smut was present 

 in the neighbourhood of that city, it is an interesting conjecture 



A. D. Cotton, Onion Smut: — A disease new to Britain, this Journal, 

 Vol. xxvi.. Xo. 2. Um. 



t Wortliington G. Smith, Diseases of Field and Garden Crops, 1S84. 



