The following article, originally published in CropWatch (https://cropwatch.unl.edu/mythbusters-southern-rust-edition/) , was written by Dr. Tamra Jackson-Ziems and Kyle Broderick. High disease levels of southern rust were present in 2025, impacting yields. This article addresses the misinformation we are hearing about southern rust before decisions are made for next year’s growing season.

“Myth #1: Overwintering Rust: The southern rust fungus cannot overwinter in Nebraska. (It cannot survive in corn residue or soil).

The southern rust fungus (Puccinia polysora) needs to infect living, green corn in order to survive, and there is no known alternate host. Thus, the fungus can’t overwinter anywhere the climate doesn’t support corn growth through the winter months. 

In fact, our rust fungi are likely blown north into the United States from subtropical locations, such as parts of Mexico, where corn is grown year-round. The southern rust fungi typically reach Nebraska in late July; however, this year they arrived earlier than usual, with the first confirmed sighting on July 9 — the earliest on record for the state.

Myth #2: Infected Grass: Southern rust doesn’t infect brome or other grasses nearby.

Rust fungi tend to have very narrow host ranges, infecting only one or a few plant species. Because several species of rust thrive under the same environmental conditions, it’s not unusual to see multiple plant species showing rust symptoms at the same time — even though they’re caused by different pathogens.

Myth #3: Super Strains: There is no new “super strain” of southern rust fungus.

… the severity we observed was due to prolonged periods of extremely favorable weather conditions — southern rust thrived under high relative humidity and average temperatures around 80°F. Southern rust…has been confirmed in 19 of the last 20 years…. If you remember 2006, you might recall another historic outbreak centered in south-central Nebraska. That season also brought delayed corn planting from spring rains, followed by ideal weather for rust development during the first two weeks of August. Many fields suffered stalk weakening and lodging, which caused memorable harvest challenges. 

Myth #4: Fungicide Failures: Fungicides did not fail to control southern rust this year.

Although yield data are still coming in, most reports indicate that fungicides performed wellagainst southern rust this year. During years with substantial disease pressure, differences in fungicide performance become more apparent, underscoring the importance of selecting effective products and applying them at the right time. Results from multiple states, compiled by the Crop Protection Network, reinforce these findings. Remember: Even the best product can’t perform well without good coverage and proper timing, especially in a season like 2025 when disease pressure was unusually high.” The full article can be viewed at: https://cropwatch.unl.edu/mythbusters-southern-rust-edition/.