CHAPTER XL 



DISEASES AND INSECTS ATTACKING CORN 



DISEASES OF THE CORN PLANT 



CORN SMUT (Ustilago mays sea). The appearance of smut in 

 corn fields is a common occurrence each year. The extent to which 

 it is found is governed greatly by the favorable or unfavorable cli- 

 matic and soil conditions which appear to have a corresponding effect 

 upon both the growth of the corn plant and that of the corn smut. 

 The damage done to the corn crop varies with the season. It is some- 

 times considerable. 



Description. Smut seldom attacks the corn plant before it has 

 reached a height of two or three feet. Occasionally, however, smaller 

 plants are affected. Small patches of a whitish color may be seen 

 swelling on the surface of the leaves, which are usually attacked 

 first. This infection in its first development may cause the leaf to 

 take on a reddish appearance. Early in the growth of the infected 

 part spots will turn from a whitish to a black color, due to the forma- 

 tion of spores. As the plant matures the infection seems to be the 

 greatest at the junction of the leaf and sheath. 



Quite frequently the tassel is found badly smutted, together with 

 the greater portion of the btalk above the ear. The first joint below 

 the tassel is probably the most common place of attack. The whole 

 ear may be affected, or only a portion of it; but after the rudimentary 

 ears are developed from the lower nodes the brace roots are the only 

 points of infection. This is due to the fact that the smut spores do 

 not penetrate any other than growing tissue. When entrance has 

 been secured a local infection sets in, the smut masses soon appearing 

 near the point of entrance. 



Some of the infection of the corn smut is brought about by the 

 spores — the black powder contained within the mass — but the infec- 

 tions are chiefly due to the Conidia which are produced from the 

 spore after germination. These are bead-like bodies which are borne 

 at the ends of short branches of a thread which protrudes from the 



