As leaves age, pustules begin to produce dark black spores instead of orange spores. These black pustules look like tar spots and are most easily seen on the lower leaf surface and leaf sheaths. Although leaf rust may initiate tiny orange spots on culms and heads, it does not form large, open pustules on these organs. This helps distinguish leaf rust from stem rust. Stem rust is uncommon and usually only occurs late in the season because it requires warm temperatures.
Stripe rust is rare in Kansas because it requires very cool weather.
Leaf rust typically occurs uniformly across a field. In overwintering locations, it is most severe on the bottom leaves. When it blows in from distant fields, it will be most severe on upper leaves. Although some strains of the leaf rust fungus can survive on jointed goatgrass or wheatgrass, they appear to be different from the strains that attack cultivated wheat. Many rusts have special alternate hosts for completion of the sexual cycle.