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Common
Rust (Puccinia sorghi) is a disease that frequents corn fields nearly
every year. However, infections and associated corn grain yield loss are usually
very minimal. Infection normally occurs from late-May to early-July. Common
rust has cinnamon-brown colored round to elongated pustules that frequently form
in bands on the lower part of the leaf, which result from infection when the
leaf was in the whorl. Common rust pustules form on both upper and lower sides
of an individual leaf, distinguishing Common from Southern rust, which
predominately sporulates on the upper leaf surface. Common
rust development requires relatively cool to moderate temperatures (54 to 82
degrees F) and nearly 100% relative humidity for about six hours. Rust
development is much more likely in pre-tassel stage corn, because a large whorl
provides a humid, protected environment, and young leaf tissue is more
susceptible to infection than emerged leaves. After tasseling, all leaves are
completely emerged (past whorl stage) and should be relatively immune to further
common rust development.
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