Disease cycle: Leaf rust develops early in the
spring on wheat grown in states farther south. The
leaf rust spores are carried by wind currents, and the
disease advances progressively northward across the
Great Plains as the wheat crops develop (Figure 4).
Leaf rust infections can lead to epidemics when environmental
conditions are favorable. The following factors
must be present for wheat leaf rust infection to occur:
viable spores, susceptible or moderately susceptible
wheat plants, moisture on the leaves (six to eight hours
of dew) and favorable temperatures (60 to 80 degrees
Fahrenheit). Relatively cool nights combined with warm
days are optimum conditions for leaf rust development.
Under favorable environmental conditions, rust spores
germinate and penetrate into the leaf. The fungus
obtains nutrients from the leaf and, within a week to