As the crop develops and matures, leaf rust generally appears on upper leaves of plants and severity increases. In North Dakota, corresponding yield losses have been as high as 30 percent for severely infected susceptible varieties, IF severe infection occured before flowering. If high leaf rust severity does not occur until the soft or hard dough stage, yield losses may range from 5 to 15 percent. Leaf rust also causes reduction of test weight, which can lower market grade and selling price. Genetically inherited resistance is an excellent means of controlling leaf rust.
Resistance limits infection and retards fungus growth and spore formation.
Resistance levels vary among the classes of wheat and among varieties within a class. Varieties with MS reaction should be used with caution as damage may occur in favorable environments. Also, the natural leaf rust population is constantly changing, as shifts in virulence or new races may occur. Varieties formerly considered resistant can become susceptible if new rust races develop. Most of the popular hard red spring wheat varieties grown in North Dakota are resistant to the prevalent races of leaf rust.