290 PLANT DISEASES 



state, such as was and is commonly practiced in the 

 prairie states of the Mississippi Valley, furnishes an 

 excellent method for spreading the rust. All the com- 

 bative measures so far mentioned are merely in the 

 nature of mild precautions. They will not always pre- 

 vent the rust and in the case of an epidemic will have 

 no effect at all in most cases. They should not, how- 

 ever, be neglected, since they constitute methods of 

 good farming regardless of the rust question. 



The most hopeful remedy for rust has yet, however, 

 to be mentioned, and this is the selection of varieties. 

 It is found where varieties of wheat differ in the time 

 of maturing one or even two weeks, that the early 

 variety more often escapes the rust than the late 

 variety. That is, the rust epidemic may come along 

 just too late to catch the early variety. Sometimes 

 an early variety may be attacked where a late variety 

 is not, but more often the early variety escapes. It 

 can usually be recommended, therefore, that early 

 varieties be planted. It is well known that the stem 

 rust of wheat is not usually so severe in the winter 

 wheat districts as it is in the spring wheat regions, and 

 in the latter regions where wheat can be grown the 

 winter wheat frequently escapes the rust on account of 

 its earliness, while the spring wheat may be attacked. 



Finally, rust may be prevented to a large extent by 

 the selection of varieties which are known as resistant 

 varieties. In wheats, as in a great many other plants, 

 different varieties give different reactions against a 

 certain disease. Some varieties may be very suscep- 

 tible to a disease, while others may resist the disease : 

 just as in human beings certain people are predisposed 

 toward certain diseases, while others, although exposed 



