DISEASES OF WHEAT 165 



DISEASES AND INSECT ENEMIES 



202. Importance. It is very seldom that a crop of wheat 

 is matured without being affected to some extent by some of 

 the common diseases to which the crop is subject, as scab, 

 rust, and smut. There are other diseases, but so little is 

 known about them that only the three named will be dis- 

 cussed here. Disease causes an immense loss to wheat and 

 other cereal crops every year, and considerable may be done 

 to check this loss. 



203. Scab. Scab is a fungous disease which attacks the 

 glumes, or chaff, of the wheat plant. It is not very common, 

 but sometimes causes considerable loss, for shrunken ker- 

 nels result when the wheat plants are affected. Usually 

 only a few glumes are affected, and these are identified by 

 pinkish spots at the base. There is no known treatment for 

 this disease, except that it has been recommended that the 

 stubble be burned if wheat is to follow a crop of wheat 

 affected with scab. 



204. Rust. Rust occasionally causes immense damage 

 to the wheat crop, sometimes ruining the entire crop of a 

 considerable part of the country. It is a fungous disease 

 which is almost always present to some extent, and which, 

 when conditions are favorable, may spread rapidly and cause 

 the straw to become very weak, resulting in shrunken kernels. 

 There are two kinds, the leaf rust and the stem rust. The 

 former is nearly always present, but the latter is by far the 

 more destructive. Stem rust may live over winter on the 

 ripened plant, or more commonly in another form on some 

 other plant. The spores may germinate and attack the 

 wheat at any stage during its growth. There is no remedy 

 known except the selection of varieties of wheat which are 

 r ust-resistant, though attempts in this direction have not as 



