1710 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



Potato, Chinese. See Sweet Potato, 

 or Yam. 



POTATO DISEASES 



Aerial Potato. See Rhizoctonia, this 

 section. 



Arsenieal Toisoning 



Spotting and dying of the foliage is 

 frequently caused by the application of 

 Paris green or other arsenical poisons. 

 It is frequently mistaken for blight and 

 injures the plant in proportion as it re- 

 duces the amount of green surface. The 

 injured foliage also offers favorable op- 

 portunities for the development and 

 spread of the early blight. 



Control 



Paris green should always be mixed 

 with lime, whether applied dry or in 

 water. It can be applied with Bordeaux 

 mixture without additional lime. Ar- 

 senate of lead can also be applied with 

 Bordeaux mixture. The latter spreads 

 and sticks better than Paris green, but 

 acts more slowly. 



New .Terse.v .\crlcultural Experiment Station 

 Circular 3."!. 



Bacteriai, Blight. See Black-Leg, this 



section. 



Bactebial Rot. See Black-Leg, this 



section. 



Black. Leg 



Bacillus phytophthorus 



Bacillus solanisaprus 



F. D. Bailey 



Black-leg, or black stalk rot, as it is 



frequently called, is a bacterial disease 



of the potato which has only recently 



become widely distributed in this coun- 

 try. It is quite probable that the disease 

 was present in certain potato-raising lo- 

 calities before 1906, but that date seems 

 to furnish the first record of its occur- 

 ence. 



The disease has been known in Europe 

 for a longer period and was recorded in 

 Canada in 1900. 



Symptoms 



An examination of plants affected with 

 black-leg will leave little chance for con- 

 fusing this disease with other described 

 potato maladies. The stem and tubers 

 are the parts attacked. The inky black 

 discoloration of the stem at the surface 

 of the ground, from which the name 

 originated, is the most constant charac- 

 ter associated with the disease. This 

 blackened area starts at the point where 

 the stem leaves the seed potato; it ex- 

 tends up to the surface of the soil and 

 in some cases may follow the stem sev- 

 eral inches higher. The illustration (Fig. 

 1) shows the result of an artificial inocu- 

 lation in which the organism followed 

 the stem up to the third leaf. 



One who is familiar with this disease 

 can detect its appearance before the 

 blackened area appears on the stem. The 

 whole plant is slightly below normal size, 

 lighter in color, with stems, petioles and 

 leaf blades erect. This condition becomes 

 more acute until finally the plant rots 

 off and dies. The seed tuber is generally 

 affected and in most cases decay starts 

 in it before the plant shows signs of 

 disease. 



