Cereals 



293 



but it is hardly probable that this disease will extend seriously 

 or become very destructive, except locally, and in very 

 humid, hot seasons. In some cases, the injury is as high as 

 6 to 10 per cent of the crop. The fungus grows in leaf, 

 sheath, and stem, rarely in the husks. Bleached or yellow 

 spots about 1 mm. in diameter first appear, and within a few 

 days darken, eventually becoming reddish-brown. Coales- 



FiG. 154. — Map showing the distribution of Physo- 

 derma zeae-maydis in the United States. Broken lines, 

 P. zeae-maydis present: solid line, P. zese-maydis caus- 

 ing damage. After Tisdale. 



cence of many spots may lead to discoloration of large areas 

 and a rusted appearance. These diseased areas are often in 

 bands across the leaf. Leaves are often killed. The dry 

 epidermis eventually ruptures over diseased spots and the 

 dusty, brown spores are freed. Diseased stems break easily, 

 resulting in considerable lodging of the corn. General san- 

 itary measures are recommended, chiefly destruction of in- 

 fested refuse and rotation of crops. 



