176 DISEASES OF ECONOMIC PLANTS 



crop in Nebraska, 50 per cent in Wisconsin, and even more 

 in Illinois. The chief seat of attack is the cane, especially 

 young ones, though the disease appears also upon both 

 petioles and leaves. 



The fungus often appears upon young canes before they 

 are 25 cm. high, making small, purplish spots, which 

 soon become grayish or dirty white in the centers. The 

 borders of the spots are purplish and slightly raised. 

 Later as the spots enlarge they coalesce, making irregular 

 blotches 2 cm. or more long, which often encircle the 

 cane. The cane then withers and dies from lack of sap 

 supply. Badly diseased canes present a bark of rough, 

 scabby appearance due to the efforts of the cane to heal 

 the wound. Canes occasionally crack from this disease. 

 The chief injury is to the cambium layer or the sappy 

 outer wood. The leaves on affected canes are dwarfed, 

 the fruit ripens prematurely, is undersized, and often 

 dries up. 



Upon the petioles of the older leaves the disease 

 appears early, spreading thence along the ribs to the leaf. 

 Owing to the one-sided attack upon the veins and petioles, 

 the leaves develop unequally, often with inrolled edges. 

 Upon the lower surface very small spots about 1 mm. in 

 diameter are produced, from which the diseased tissue 

 often falls. In the older diseased spots the spore-bearing 

 acervuli arc just visible to the naked eye. 



Occasionally the disease, even though bad, may escape 

 observation during the first and second years, and even 

 well into the third year. Then, with prospect of a good 

 yield, the berries may shrivel on the stems and later many 

 plants may die. More often the disease remains moder- 



