THE BLACK STEM RUST 
387 
cannot reproduce on the barberry, but on being blown to 
the grains or certain grasses, they begin a new stage in the 
life history of the red rust. These propagate on the grain 
in the field as before. Another source of infection is the 
summer spores which may have lived over the winter on the 
grasses near the field, or 
on straw or stubble. A 
summary will put the his¬ 
tory clearly: (1) the red 
or summer spores spread 
the disease from wheat 
to wheat, or from wheat 
to grasses and back to 
wheat; (2) the winter 
spores formed on wheat 
or grasses in the autumn 
remain on them until 
spring when, by means of 
sporidia, the infection of 
the common barberry 
takes place ; (3) the clus¬ 
ter cups or spring spores 
on the barberry start the 
infection again on the 
wheat and grasses. 
Conditions Favoring the 
Rust. — Cool nights with 
heavy dews, followed by 
hot muggy days, afford ideal conditions for the growth of the 
disease. Any condition which favors the growth of the grain 
and retards that of the rust is unfavorable to the disease. 
Methods of Control. — No sure means has been found of 
curing the disease, but experiments have proved that there 
are several ways of reducing the amount of damage done by 
it. Among them may be mentioned clean cultivation, 
Figure 355. — Diagram of Life History 
of Red Rust of Wheat. 
