142 Journal of Agricultural Research voI.xvi.no. s 



as to whether these conditions are realized to any great extent in the 

 Northern States, and it is hoped that the disease will not become a 

 serious one in the Corn Belt. 



(7) The rare occurrence or absence of the disease farther west is no 

 doubt due to the semiarid conditions which exist there. The moisture 

 requirements suitable for the development of an epidemic of the disease 

 perhaps are seldom, if ever, realized in this section. However, further 

 investigations are needed to determine in detail what the weather condi- 

 tions are for the given sections and to study the possibilities for further 

 development and spread of the disease in the Com Belt. 



HOSTS 



So far as is known, all varieties of corn, including pop corn and sweet 

 corn, are susceptible to the disease. Of the numerous varieties obsei-ved 

 in the South there seems to be little, if any, difference in the degree of 

 susceptibility shown by them. P. zeae-maydis also occurs on teosinte 

 (Euchlaena mexicana), a near relative of the corn plant. It is possible 

 that the disease was introduced from Mexico or Central America with this 

 plant. The fact that it has been found in considerable quantities on 

 corn in comparatively isolated fields where corn was never grown before 

 and where no corn products were applied to the land suggests the possi- 

 bility that there are other hosts for the fungus among wild plants. 



SIGNS OF THE DISEASE 



The disease occurs on the blade (PI. A), sheath, and culm (PI. B),and 

 in rare cases it has been seen on the outer husks of the ears. Infection is 

 usually more abundant on the lower half of the plant. Its first appear- 

 ance on the thin parts of the blades resembles the early stages of the 

 corn rust caused by Puccinia sorghi. It is first evidenced by slightly 

 bleached or yellowish spots, which become darker within a few days when 

 sporangia are formed. This darkening continues until the spots are 

 brown to reddish brown, with a somewhat lighter margin. These spots 

 are very small, seldom becoming more than i mm. in diameter, except 

 where two or more of them coalesce. The spots may m some instances 

 be so numerous as to give the entire blade a rusty appearance. For this 

 reason the disease is often considered a true rust by persons who are not 

 familiar with its nature. This rusty appearance is not uncommonly 

 seen in bands across the blades, owing to the nature of infection, which 

 takes place through zoospores in the bud water. On the midrib of the 

 blade and on the sheath the spots become considerably larger. Often a 

 single spot will measure 0.5 cm. across. They are irregular in shape and 

 sometimes may be almost square in outline. This is due to the fact that 

 they are definitely limited by the cell walls. In the very early stages 

 these spots are evidenced by a color which is a somewhat darker green 

 than the normal tissue surrounding them. This seems to indicate a 



