DISEASES OF WHEAT 167 



rust spores to the heading wheat. That the spores are thus 

 brought to the wheat is shown by the fact that screened plants 

 are not rusted, and that distilled water exposed to the air will 

 gather great numbers of the spores in the short period of a 

 half hour. The more soft and succulent the wheat straw is, the 

 more open it is to rust infection. "The most effective rust in- 

 fection weather may be described as muggy, showery, sultry, 

 rather still hot days, with foggy, cool, dewy nights, at about 

 the blossom period. Just following the infection, cool, moist, 

 slow growing, showery weather may result in the most general 

 rust infection, and in the greatest breaking out or rupturing of 

 the straw." 



How Damage Results. Rust deprives the wheat grains of 

 their nourishment. The grains may be only slightly shriveled, 

 or the crop may be completely ruined. It has been claimed that 

 orange leaf rust does little damage to wheat, and that in very 

 wet seasons it may even be of benefit to the grain by preventing 

 superabundant growth of the vegetative parts. This has been 

 denied recently, however, and with good show of reason. It is 

 pointed out that in 1904 and 1905 the leaf rust was so severe 

 that the wheat grains wilted and shriveled before the stem 

 rust was well developed on the straw. The leaf rust may also 

 delay the ripening of the crop until injury from frost results. 2 

 Since the attack of the stem rust is the more direct, it is un- 

 questionably the more virulent. 



The Loss From Wheat Rust in the United States doubtless 

 exceeds that caused by any other fungous or insect pest, and it 

 may be greater than the loss from all other diseases combined. 

 It is often not noticed because it is light. In one or another of 

 the wheat growing sections, great areas are partially to nearly 

 completely destroyed each year. While almost fabulous figures 

 are required to record the estimated annual loss, the proba- 

 bilities are that this is underestimated, for the slight, unnoticed 

 attacks never enter the computation. If the loss is but 1 per 

 cent of the wheat crop, it approximates $5,000,000 annually in 

 the United States alone. Bolley examined the wheat fields of 

 North Dakota for fourteen seasons, and, leaving out of con- 

 sideration the years of great destruction, he estimated the 



1 N. D. Bui. 68 (1906), p. 655. 



2 N. D. Bui. 68 (1906), pp. 651-654. 



