FUNGI AFFECTING THE SWEET POTATO 



The BJack Rot 



Ceratocystis fimbriata 



There are several kinds of ^'rot" affecting the sweet 

 potato, which have been carefully studied by Dr. Byron 

 D. Halsted, of the Kew Jersey Experiment Station. To 

 liis studies we are indebted for much of the following 

 information upon the subject : 



According to Messrs. Ilalsted and Fairchild, ^^the 

 most conspicuous sign of the present disease, and the 

 one w^hich distinguishes it from other diseases, occurs 

 upon the potatoes themselves. It consists in the j^res- 

 ence of dark, somewhat greenish spots, varying from a 

 quarter of an inch to four inches in diameter, sometimes 

 covering the greater part of the I'oot and extending some 

 distance into the tissue. Tliese sj)ots, wdien once seen, 

 can not be mistaken, as they are simply sunken areas 

 with distinct margins, like spots burned into the potato 

 with a metal die, which has left the skin uninjured. 

 Should the slightest doubt, as to the identity of the dis- 

 ease remain, after a superficial examination, the removal 

 of a small portion of the skin, exjoosing the olive-green 

 tissue below, would dispel it. Among the sprouts, or 

 young plants grown in hotbeds, the disease manifests 

 itself in dark lines upon the lower portion of the shoot; 

 and sometimes of the lower leaves, giving rise to the 

 name of '^ black shank" among the growers. These 

 dark lines or blotches often appear upon etiolated por- 

 tions of the stem, and are almost black in color. In 

 very severe cases the tip of the sprout wilts and dies. 



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