-1-

Purdue University
Agricultural Extension Service
Dept, of Botany and Plant Pathology

Mimeo BP-86
June 21, 1955

LEAF RUSTS OF WHEAT AND OATS
Ralph M. Caldwell and John F. Schafer

The most serious diseases of the wheat and oat crops of Indiana,
over the years, have been the leaf rusts.

Losses caused by leaf rusts
Leaf rusts reduce the grain yields of wheat, oats, and other small
grains by damaging the leaves of the plants. The degree of loss depends
on the amount of rust developing and further on how early the plants
are attacked. Experimental work with leaf rust of wheat has shown
that rust losses on susceptible varieties may reach 30 percent of the
potential yields when the severity of infection reaches 100 percent
leaf coverage within a week after heading. When susceptible varieties
are grown, the average annual losses run about five percent.

Infection by leaf rusts
Leaf rust spores may be blown into Indiana from the States to
the south, or, the rust may sometimes live over winter within the
States on winter grains when plants become infected in the fall. In-
fection occurs when moisture is present on the plants for a few hours.
Dew provides excellent conditons for infection. With common late
spring temperatures, rust develops on the leaves 10 to 14 days after
infection. Following this initial development of rust, reinfection
occurs every suitable dewy night. The earliness and numbers of spores
blown in from the south combines with the number of fall infections
which overwinter within the State and the subsequent abundance of heavy
dews are the main factors which determine the final severity of the
leaf rust diseases.

Leaf rust of wheat
The leaf rust of wheat has been found in moderate to heavy
amounts on susceptible varieties throughout Indiana in 1955. Fields
of Vigo wheat, which is resistant to many strains of the rust, vary
in their reaction. Most Vigo fields observed have been nearly free
from rust even where nearby fields of susceptible varieties are
heavily infected. Other Vigo fields have developed moderate rust.
It is suspected that where rust has developed on Vigo wheat,
overwintering and therefore an early abundance of a Vigo attacking
rust strain probably occurred. Knox wheat which is highly resistant
has been free from leaf rust.

Control
The only practical control of leaf rust is the growing of resistant
varieties. To control leaf rust of wheat a resistant variety such as