Southern Rust is caused by the fungus Puccinia polysora.  The fungus originates in southern states in more hot and humid climates.  As the diseases progresses, it asexually produces urendiniospores which can be carried by the south easterly winds commonly seen in the summer months in the eastern half of the United States. The urendiniospores are carried to the north into the heart of the corn belt and in some years as far north as Canada.  Southern Rust becomes most prevalent usually in the later growth stages of corn and in the months of July and August.  If conditions are favorable, the disease can be devastating to corn leaf tissue and over all yield.

Unfortunately, the symptoms of southern rust are very similar to those of another fungus, common rust.  Southern Rust tends to develop on the upper side of leaves and the rust pustules in most cases are much smaller than those with common rust.  Common rust lesions are usually elongated, larger, and on both sides of the leaves.  Southern Rust is more dense when producing pustules as well.  Early leaf infections of southern rust are usually circular or oval in shape and develop a light green or yellow halo at the margins.  As the lesions develop, the fugus will explode through the epidermis of the leaf releasing orange urendiniospores that can be rubbed off  when the leaf is ran between 2 fingers. 

Both Southern Rust and Common Rust can be effectively treated with foliar applied fungicides.  Genetic resistance is another common source of reducing issues with this fungal disease.  Head to our technical product breakdowns to check out the southern rust ratings on hybrids or contact your local STAR Partner dealer or Technical Team Agronomist.

Photograph by Caleb Pokorny, LG Seeds.

Sources :

1. https://cropprotectionnetwork.org/resources/articles/diseases/southern-rust-of-corn#:~:text=Southern%20rust%20is%20caused%20by,on%20the%20upper%20leaf%20surface.
2. https://cropwatch.unl.edu/plantdisease/corn/southern-rust