Image Courtesy of:
http://vegdis.cas.psu.edu/VegDiseases/identification/scscr.html

Last updated by
Nick Dolezal
on April 16th, 2002

Common Names of Southern Corn Rust:

    -Rust
    -Leaf Rust
    -Corn Rust
    -Southern Corn Rust

Fungal Causal Agent:

Species:
    Puccinia polysora Underw.

Class:
    Basidiomycetes

Order:
    Uredinales

Host Range:

     Here are some of the alternate crops, ornamentals, and weeds that southern corn rust can survive on:
 

Geographical Range:

     Southern corn rust can be found generally through the southern U.S and further south wherever corn is grown in warm/humid regions. 

Symptoms:

     As seen on photo at the top of the page, southern corn rust can be detrimental to photosynthesis and overall productivity of a corn plant.  The most obvious symptoms are dark, reddish pustules which can be scattered over the top of corn leaves. This is a major difference from Northern corn leaf rust where pustules can form on the upper and lower surface of leaves.  These pustules can be found on corn husks but are generally found on the leaves. Southern rust pustules are smaller, more round and reddish in color when compared to common rust. 

Dissemination:

     The plant pathogen being examined here is generally carried to other plants by wind.  Strong southerly winds carry spores to infect susceptible fields in other areas.  Infected plant material which is transported on machinery can also allow for primary inoculum to spread to new areas.  However, southern corn rust spores don't survive the midwestern winters on crop residue. 

Disease Cycle:

     Southern rust develops more quickly and is more detrimental to leaves than common rust.  Uredo spores are blown as primary inoculum and infect northern corn fields if the temperature is right for development. Southern rust is favored by periods of high relative humidity and high temperatures, usually, between 80 and 90 degrees F.  The disease can develop very quickly during hot, moist conditions.  Southern rust occurs generally later in the year and is more common in southern states. Southern rust incidence is not as common as common rust, but the effects on corn fields are more severe when it is present.  Click here for a complete disease cycle of Southern Corn Rust.

Control Measures:

      Southern corn rust rarely needs control as the pathogen is hit or miss in northern states.  Most problems with common rust are not serious enough to warrant control.  If a problem area has been identified however, southern leaf rust resistant hybrids are available.  Fungicides are available for rust control for areas with extreme problems.  A farmer may consider planting as early as possible in the season so as to ensure plants will be more developed if conditions warrant rust development.  

Recent Research-Summary:

Related Journal Article:

Holland,-J.B.; Uhr,-D.V.; Jeffers,-D.; Goodman,-M.M. 1998.  Inheritance of resistance to southern corn rust in tropical-by-corn-belt maize populations.  Springer-Verlag.  96:232-231.

    The reason for the study performed here was observe the resistance inheritance within several corn populations to southern corn rust. The study was accomplished by crossing two temperate inbred lines to a susceptible dent hybrid.  The inbred lines had good ratings of  resistance to Puccinia polysora.  Hybrid resistance was measured by counting pustules on seedlings that were grown in a greenhouse. Neither source of resistance was completely effective against southern corn leaf rust which prevented determination of the alleles of the two genes suspect for resistance.  It was determined that both sources of inbred lines had better resistance to southern rust than the susceptible hybrids.

Sources:

Agrios, George N. 1997.  Plant Pathology 4 ed.  Academic Press.

Pioneer Web site.
     http://www.pioneer.com/crop_management/corn/rust_southern_common.htm
 

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