Help your growers avoid a southern rust corn calamity—and possible yield losses of up to 45%—by calmly and clearly advising them on fungicide for rust ahead of this disease’s arrival.¹ Generally, treatment is most effective at VT stage, which happens around mid to late July.
As a trusted adviser, you can assist growers by interpreting disease pressure maps, recommending fungicides with multiple modes of action and determining the economic ROI of treatment depending on the crop’s growth stage and environmental risks.
Here’s what you need to know to support growers in treating southern rust in corn before it escalates.
Consult regional monitoring and alert tools
A free online tracker from university experts, such as the Crop Protection Network’s Southern Rust of Corn Map or ipmPIPE’s Current Map for Southern Corn Rust, can help you keep tabs on encroaching corn rust in neighboring counties. Your local county extension office can also be a valuable resource.
If corn rust is detected in an adjoining county, it’s important to be vigilant. Southern rust spreads rapidly via wind currents. The disease presents as numerous small and round pustules on the upper part of leaves that leave orange or tan streaks on your fingers when rubbed off.²
It’s most common when temperatures hover between 77 F and 82 F, with at least six hours above 95% relative humidity.³
You can also share this free fungicide efficacy tool from Crop Protection Network with your growers so they can start evaluating fungicide for rust treatment options.
Talk through evaluation timing, efficacy and modes of action
Explain to your growers that for maximum disease suppression and economic return, it’s important to target fungicide applications between corn’s tasseling (VT) and milk (R3) growth stages.
Recommend fungicides such as BASF’s Veltyma® fungicide or Headline AMP® with multiple modes of action. With these products, your growers can experience southern rust control that typically lasts beyond the two-week protection period that often comes with a single mode of action.⁴
Explain the growth stage cutoff for fungicide efficacy
Your growers should be aware that applications of fungicide for rust fungi after milk stage rarely pencil out. That late in the season most grain fill is done, and the potential gain in yield protection isn’t substantial enough to recoup the cost of fungicide, fuel and time needed for treatment.
At the same time, later applications might reduce your growers’ losses from low test weight and lodging. As with any decision, advise your growers based on their unique situation.
Help growers fight southern corn rust damage throughout the season
Work with your growers through the dent stage (R5) to monitor and manage around southern corn rust damage. The disease has a tendency to reduce test weight and damage stalk integrity, which creates greater risk of lodging.
If this persists at harvest, consult extension resources on harvesting fields with southern rust for specific combine settings that can help.
Experts are available to help you and your growers make their southern rust corn treatment decisions. Reach out to a nearby extension office agent or your regional BASF representative.
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Endnotes
- Jackson-Ziems, Tamra, and Jenny Brhel. “Corn Disease Update: Fungicide Expectations for Disease Control.” CropWatch, University of Nebraska–Lincoln Institute of Agriculture and Natural Resources, 15 Aug. 2024,https://cropwatch.unl.edu/2024/corn-disease-update-fungicide-expectations-disease-control/. Accessed 24 Mar. 2026.
- Duffeck, Maíra. “Corn Disease Update – July 14, 2025.” Oklahoma State University Extension E-Pest Alerts, July 2025,https://extension.okstate.edu/e-pest-alerts/2025/corn-disease-update.html. Accessed 24 Mar. 2026.
- Jackson-Ziems, T. et al. “Corn Disease Update: Fungicide Expectations for Disease Control.”
- Mueller, John. “Fungicides and Southern Rust in Corn.” Clemson University Cooperative Extension Service Blog, 11 June 2021,https://blogs.clemson.edu/sccrops/fungicides-and-southern-rust-in-corn/. Accessed 24 Mar. 2026.
