In early July, southern rust caused by the fungal pathogen Puccinia polysora was discovered in Hall, Adams, Clay, Fillmore,  Thayer, and Burt counties in Nebraska.  Most farmers in south-central Nebraska remember the corn season in 2006 walking out of fields orange and the slow harvest due to downed stalks.  Since then, southern rust has been a disease of concern and fungicides are used to prevent and also treat it when it’s found in fields.  

I promised when we were first discovering southern rust this year that I’d post pics, so while delayed, here they are!  It is often confused with common rust which we see earlier every year.  Common rust typically has pustules (raised fungal spores) that are brick red in color, larger, and on the upper and lower leaf surfaces.  The pustules tend to be more spread out.  

Southern rust typically has very small pustules that are clustered on predominately the upper leaf surface and are tan to orange in color.  This year, southern rust pustules tend to be more tan in color than orange but are still distinctively different with their smaller and clustered appearance.  Both fungal rust pathogens arrive in Nebraska each year via wind from the south.  Southern rust prefers warm, moist conditions which, in spite of our dry spell, is typical within our pivot and gravity-irrigated fields in the area.  At this time we are recommending if you find southern rust in your field to consider treating with a fungicide.  Please be sure to read and follow all label directions including paying attention to pre-harvest intervals.  A list of corn fungicides and efficacy can be found here by scrolling down to the corn section.

Additional information and pictures of these diseases can be found here.