BULLETIN No. 194. 



CONTROL OF THE BLACKLEG OR BLACK-STEA^ 

 DISEASE OF THE POTATO. 



W. J. MoRSS. 



Bulletin 174 of this Station, issued December, 1909, discussed 

 the character and appearance, means of distribution, distribu- 

 tion in America and economic importance of the blackleg dis- 

 ease of the potato. At the same time methods for prevention 

 and eradication were outlined and discussed. It was then stated 

 that these recommendations were made on more or less empiri- 

 cal grounds and were not based upon regularly conducted ex- 

 periments. It is now proposed to give the results of certain 

 field trials and experiments whereby these recommendations 

 were tested on a large scale under actual farm conditions. 

 Before taking up the details of these experiments and the results 

 obtained therefrom it is perhaps best to summarize some of the 

 more important parts of Bulletin 174 and to give a brief account 

 of certain preliminary studies which led up to the experiments 

 mentioned. 



"Blackleg," "black-stem," "black stalk-rot" or "stem-rot" is 

 a bacterial disease which attacks both the stem and tuber of the 

 Irish potato. Various investigators, mostly in Europe, have 

 isolated from the diseased plants and described under different 

 names bacteria which were again capable of causing very similar 

 effects upon the host upon inoculation.* Hence so far as our 

 present knowledge goes blackleg, strictly speaking, is a general 

 term applied to a type of bacterial disease which attacks and 

 destroys the base of the potato stem, producing a characteristic 

 blackening of the diseased tissues, rather than a term applied 

 to a single disease caused by a specific organism. However, the 

 organisms are so near alike and are so nearly identical in th.eir 



* B. phytophthorous Appel, B. solanisaprns Harrison, B. atrosepticus, 

 van Hall, B. melanogenes Pethybridge and Murphy, etc. 



