CHAPTER XIX 

 DISEASES AND INSECT ENEMIES 



THE three wheat diseases causing most damage are, in probable 

 order of importance, rust, smut, and scab. 



Rust. Rust is found in all wheat regions, but is most injurious 

 in the humid regions. In dry seasons the damage is usually not 

 great, but occasionally in a wet season will cause almost complete loss 

 of crop over large areas. While all rust has similar appearance on 

 the plant, there are really two kinds the leaf rust or " red rust " and 

 the stem rust. Stem rust is most destructive. It may live over 

 winter on old stubble, or straw, and probably on young winter wheat 

 plants. The growing wheat may be affected at any time, but usually 

 weather conditions are most favorable about two or three weeks before 

 the wheat is ripe. There are no known remedies for rust except to 

 choose rust-resistant varieties, as varieties vary in this respect. 



Smut. There are two kinds of wheat smut. The most de- 

 structive is known as bunt, or stinking smut, and the other as loose 

 smut. They differ in these respects : ( 1 ) The bunt destroys only the 

 kernel, leaving the glumes intact, while loose smut destroys both 

 grain and glumes, leaving only a bare rachis. (2) When mature 

 the spores of the bunt usually remain intact in the grain, making 

 the characteristic " smut balls " found in the threshed grain. The 

 loose smut breaks up and the spores are scattered while the grain is 

 standing. 



Infection. It is important to note the difference in infection of 

 the two smuts and the resulting different method of treatment neces- 

 sary. (1) The bunt smut balls are broken up more or less during 

 harvesting and threshing and the loose spores find lodgement on the 

 outside of grains and remain on the outside, especially among the 

 hairs at the upper end or in the crease. ( 2 ) The loose smut matures 

 at about the time the grain is in blossom. The spores are at once 

 spread, and, lodging on young seeds just forming, germinate and 

 penetrate to the inside of the seed, where the smut remains dormant 

 until germination. 



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