EXERCISE 85 

 WHEAT RUST A DESTRUCTIVE PARASITE 



Materials. Stems and leaves of rusty wheat or oats, collected 

 just before harvest ; wheat plants or stubble showing black rust, 

 collected in late summer or autumn ; leaves of barberry showing 

 rust. 



Directions for work. 1. Red rust. Study the distribution, 

 shape, and general appearance of the red spots on both stem 

 and leaves of the wheat plant. Write a description intended to 

 assist in identifying the disease. Scrape out some of the con- 

 tents of one of the red spots and examine under high power of 

 microscope. Add to your description the facts you discover. 



If possible, examine rusty grain in the field to determine the 

 character of the injury by rust. Note especially the effect upon 

 the general vigor of the plant, the strength of the straw, and 

 the quality of the grain. If you cannot visit fields at this time, 

 question farmers and others on the above points. 



Find out, by reading and by talking to practical farmers, about 

 the effect of weather conditions upon rust and about the sus- 

 ceptibility of different varieties of wheat, oats, and other grains 

 to rust. Does the information from all sources appear to be 

 equally reliable ? Sum up what you find to be the facts on 

 this topic. 



2. Black rust. Study in manner similar to that outlined for 

 the red phase. The black rust is the same plant as red rust, 

 but a different kind of spore is produced later in the summer. 

 As this phase appears after harvest, little damage can be done 

 directly. Note dates of collection of red and of black rust. 



If you can examine these spores microscopically, note their 

 characteristics in comparison with the red-rust spores. Are they 

 in any way particularly fitted for the season of the year which 

 follows the time of their production ? 



3. Rust on barberry. The " cluster cups " of wheat rust may 

 be found on the under side of barberry leaves. Study and de- 

 scribe sufficiently for identification. Smaller growths of the 

 fungus may be detected upon the upper side of the leaves. 



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