I I 



POTATO WILT, LEAP-EOLL, AND RELATED DISEASES. 5 



with the leaf-roll group, but the writer has not seen this disease and 

 has been unable to arrive at a satisfactory conclusion concerning its 

 relationship to any known American trouble. The causal organism 

 has not yet been properly described. 



A second bacterial disease of German potatoes is referred to by 

 Spieckermann (1911) as different from Appel's ring disease. This 

 the writer saw at Muenster and found to be unlike any of the well- 

 known American diseases. 



FUSARIUM WILT. 



DESCRIPTION OF DISEASED PLANTS. 



The distinctive characteristics of this disease are a rolling or wilting 

 of the leaves, premature death of the foliage, and the occurrence of 

 the fungus Fusarium oxysporum (Schlecht) Sm. and Sw. in the lower 

 part of the stem, in the stolons, and frequently in the tubers also. 



In detail, the appearance of potatoes attacked by Fusarium wilt 

 varies according to the severity of the infection, the age of the plants, 

 and the variety. 



The time of onset varies with the degree of infection. Where 

 diseased seed stock has been used, there is often defective germina- 

 tion and an irregular stand of plants of uneven size. As a rule, 

 however, the disease is not noticeable till the plants are a foot or 

 more high, and in most cases it does not become generally prevalent 

 till midsummer, whUe it is characteristic of moderate infections that 

 the plants die only two or three weeks in advance of their normal 

 time of maturity. 



Wilting of the foliage is to be observed in the more rapid types of 

 the disease, but is less marked than in some other Fusarium wilts, 

 such as that of watermelon, for instance. 



The name ''wilt" has been retained because it is in common use 

 for this and related maladies, though the name "Fusarium blight of 

 potatoes" has also been applied. The foliage symptoms may be 

 described by either term. They are those of a plant whose water 

 supply has been gradually shut off by fungus invasion of the lower 

 stem. 



The lower leaves droop and die first, the upper ones wither or wilt, 

 and the entire plant dies prematurely. (PI. I.) The leaf-roll that 

 accompanies wilt differs from the true leaf-roll in that the former 

 lacks turgidity and the leaves die within a few days. 



The color of plants in the first stages of wilt may be a lighter green 

 than is normal. This frequently turns to yellow, especially if the 

 progress of the disease is slow, when the entire plant becomes yellow 

 and the field takes on a very spotted appearance. It is different 

 with the true leaf-roll, where the yellowing is, in the American types, 

 more confined to the upper leaves and is accompanied on many 



