328 Diseases of Truck Crops 



wilt is prevalent. In Michigan, Illinois, Wisconsin, 

 and Minnesota, Fusarium wilt is found in the older 

 potato districts. The trouble is also found in Colo- 

 rado and Utah where it thrives on irrigated as well as 

 on dry lands, on sandy loams as well as on the heavier 

 clays. 



Symptoms. When infected seeds are planted, the 

 result is a poor germination and uneven stand. The 

 disease however does not attract attention until the 

 plant attains a height of a foot or more. 



Wilt is characterized by a drooping of the lower 

 leaves, which are first to die. This is followed by a 

 wilting of the upper foliage and by a premature dying 

 of the tops. The leaf roll that is noticed in Fusarium 

 wilt differs from true leaf roll in that in the former 

 the leaves lack the turgidity and soon die as a result 

 of the infection. Wilted plants are at first light green, 

 then yellow, finally drying up and dying. The disease 

 first gains entrance through the tender rootlets in the 

 soil, gradually working up into the main roots, stolons, 

 tubers (fig. 62 e, f), and some way into the stem. In 

 splitting open a diseased stem, the interior water 

 vessels are found to be slightly browned. But few 

 Fusarium spores are formed on the dead stems. In 

 the tubers the presence of wilt is indicated by a 

 browning of the vascular rings. 



The Organism. The microconidia are pedicellate, 

 sporodochia and pseudopionnotes present, macro- 

 conidia 4 to 5 septate, pinkish buff color in mass 

 (fig. 62 g, h). Bluish black sclerotia are formed on 

 potato plugs. For methods of control see p. 337. 



