Cereals 291 



plants show decayed roots and purplish-brown discolored 

 stalks when split lengthwise. 3. Down-stalks due to rotting 

 of the roots, so that the plant falls over. 4. Broken stalks 

 due to weakening, chiefly at the nodes, 5. Barrenness and 

 nubbin formation. The infected plant lacks vitality to form 

 a perfect ear. 6. Broken shanks due to rot. 7. Diseased 

 kernels. The kernels may be molded and cracked, though 

 no sign of disease may be apparent and the infection or 

 weakening of the kernels shows only on germination. The 

 severity of the attack depends upon the stage of develop- 

 ment, the vigor and resisting power of the corn plant as 

 determined by the conditions for growth and development, 

 and by its heredity. 



Root-rot is caused by fungi, mainly Fusarium, and arises 

 chiefly from primary infection, from infected seed, though to 

 some extent from secondary infection in the field. The 

 planting of infected seed is largely responsible for missing 

 hills, down-stalks, nubbins, and other signs of disease. 



No infected corn should be used for seed. To eliminate the 

 infected seed, special adaptation and care in using the rag- 

 doll tester, or the use of special testers, devised by Hoffer, is 

 necessary, whereby the seedlings that show infection, when 

 less than three inches in height, may be recognized and the 

 ears from which they originated discarded. 



Since the wheat scab organism (Giberella) causes rot of 

 stem and shank of corn, corn so diseased increases the amount 

 of wheat scab in succeeding crops. 



Wilt ^^'^- ^^^ (Pseudomonas stewarti EFS.). — This corn wilt 

 was first described by Stewart as prevalent in nearly all parts 

 of Long Island upon many different varieties of sweet corn. 

 In some cases the entire crop was ruined, and 20 to 40 per 

 cent of loss was frequent, though in the majority of cases the 

 loss was so slight as to pass without notice. It has been 

 noted on sweet corn in Kentucky and Illinois, but rarely on 

 field corn. 



The diseased plants wilt and dry up much as though from 

 lack of water, yet in soil that is amply supplied with water. 



