Southern rust, a fungal disease, can reduce nutrients and lower digestibility in infected corn fed to livestock, says University of Missouri Extension field agronomist Nick Wesslak.
Early dry down caused by southern rust can cause problems with proper silage packing, which increases risk of poor fermentation and higher mold and yeast populations.
Corn infected with southern rust may be more of a concern for the dairy industry than the beef industry, says Eric Bailey, MU Extension state beef nutrition specialist. The dairy industry relies heavily on corn silage, and milk production is highly sensitive to subtle changes in nutritive value.
Leads to other diseases
While southern rust (Puccinia polysora) does not produce known mycotoxins, it opens the door for other stalk and ear rot diseases that produce mycotoxins in corn-based feedstuffs such as silage, grain and stover, says MU Extension veterinary toxicologist Tim Evans.
He recommends running a mycotoxin panel screening before feeding forage or grain infected with southern rust. Producers also should consider diluting with clean feedstuff and using other mycotoxin mitigation strategies as needed.
Southern rust spreading in Missouri
Southern rust was found in 25 Missouri counties in the 2025 growing season, according to the Corn IPM Pipe, a collaboration of many universities.
The wet start of the growing season contributed to southern rust being confirmed earlier than usual.
Southern rust grows well in warm weather (77-88 F) and high humidity. It is identified by orange to brown raised lesions on the top leaf surface, and yellow flecking on the leaf underside, but no pustules, says MU Extension plant pathologist Mandy Bish. Open lesions leave an orange to brown mark on fingers when touched or rubbed.
Looks like common rust
Southern rust and common rust symptoms are similar, and the diseases are difficult to distinguish in early stages. It also is common to see both pathogens infesting the same leaf, says Bish.
Wesslak recommends sending samples to a diagnostic lab, such as the MU Plant Diagnostic Clinic, to determine which species are present when symptoms first arise.
Neither rust species overwinters in the Missouri. Both move northward from tropical areas as the growing season progresses.
Source : missouri.edu