CoLOlfADO l^LANT DISEASES 
53 
Stem Rust of Wheat, Oats, Barley, and Rye (Puccinia graminis) 
— Each cereal has its own specialized form of stem rust which can 
affect none of the other cereals. Each 
form, however, can affect a number 
of wild grasses. Elongated reddish 
brown blisters break open and amass 
of red rust-colored spores are set free 
to be blown about by the wind for 
long distances. When these fall on 
the proper host under the proper con- 
ditions they germinate and produce 
new rust spots. Later in the season 
black spores are formed in the rust 
spots instead of the red spores. These 
black spores have thick walls and 
may live over the winter while the 
red spores have thin walls and sur- 
vive the winter only in very mild 
climates. The black spores do not 
germinate until spring and then can 
not infect any of the cereals. They 
do, however, infect the common bar- 
berry shrub. On the leaves of the bar- 
berry they produce yellowish or 
orange colored spores. These yellow 
spores produced on the barberry cannot infect the barberry but are 
blown back to the cereals and grasses where they again produce the 
red spores. 
The rusts cannot be controlled by any known method of spraying 
or seed treatment and little success has rewarded efforts to develop 
resistant varieties. The eradication of the common barberry from 
which the rust gets its start in the spring gives more promise for 
success than any other method. Losses from this rust have been 
successfully avoided in Denmark since 1903 by this measure. The 
United States Department of Agriculture has underway a campaign 
to destroy all common barberries in the wheat growing sections of 
the United States. Many bushes have already been destroyed. Learn 
to recognize the barberry bush and if you have one on your property 
destroy it. Write to the Agricultural College for further in- 
formation. 
Leaf Rust of Wheat (Puccinia triticina) — Leaf rust as the name 
indicates commonly occurs on the leaves and is never as destructive 
Black stem rust of wheat. 
