Ethan Carter, UF/IFAS Extension Regional Specialized Agent Row Crop IPM; Dr. Bob Kemerait, UGA Plant Pathologist, Dr. Ian Small, UF/IFAS Plant Pathologist  
Southern Rust of Corn

Southern Rust of Corn found in Calhoun County on 6/9/2023.  Credit:  Caleb Traugh, Traugh Ag Services

Many of the Panhandle’s March planted corn fields are now well into tassel stage (VT).  From tassel to milk stage (R3) is a key period during the season when it is critical to prevent yield loss due to disease. It is very important for growers to scout and consider disease pressure leading up to these critical growth stages.

Southern rust is one of the most concerning corn diseases for our area and as of today it has been confirmed in the Florida Panhandle. Yield losses up to 45 percent have been reported with severe disease. Timely fungicide applications can usually save 5-10 bushels/Acre, with applications between the silking (R1) and milk stage (R3) providing the most yield savings. According to UGA’s Extension Pathologist Bob Kemerait, early onset southern rust can have the potential yield loss of 100 bu/A, if left untreated. Additional applications may be needed for season-long crop protection, depending on the timing of disease onset and the intended use of the corn i.e. grain vs silage. Applying a fungicide to field corn within two weeks (50 percent starch line) of physiological maturity (black layer) is unlikely to provide an economic benefit.

An excellent resource for fungicide efficacy on corn diseases with an extensive product list is provided by the Corn Disease Working Group (page 2). There are many labeled products available, each with strengths and weaknesses relating to different diseases. Products with mixed modes of action tend to have a longer protective window compared to those with a single mode of action. Mixed modes of action tend to provide better efficacy and more robust disease protection, as well as reducing the risk of resistance development. Use the link above to compare product efficacies for southern rust.  Some example products with single and mixed modes of action that have southern rust activity are listed below.


Example products with mixed modes of action include:
  • TrivaPro 2.21 SE (13.7 oz/A)
  • Headline AMP 1.68 SC (10-14.4 oz/A)
  • Veltyma (7-10 oz/A)
  • Approach Prima 2.34 SC (3.4-6.8 oz/A)
  • Stratego YLD 4.18 SC (4-5 oz/A)
  • Delaro Complete 3.83 SC (8-12 oz/A)

Example products with single modes of action include:
  • Tebuconazole (4-6 oz/A- depending on product)
  • Headline 2.09 EC/SC (6-12 oz/A)
  • Quadris 2.08 SC (6-15.5 oz/A- depending on product)
  • Domark 230 ME (4-6 oz/A)

Southern corn rust image

Typical southern rust signs with orange to light brown, small and densely packed pustules on the upper leaf surface. The lower leaf surface has yellow flecks and very few if any pustules. These symptoms and signs can distinguish southern rust from common rust.

For additional information about Southern rust of corn use the following link for the Southern Crop Protection Network’s Southern Corn Rust Disease Management Guide.  For other information, contact your local extension office.

Ethan Carter