The Indiana Certified Crop Adviser panel includes Gene Flaningam, Flaningam Ag Consulting, Vincennes; Carl Joern, Pioneer, Lafayette; Greg Kneubuhler, G&K Concepts, Fort Wayne; and Dan Quinn, Purdue University Extension corn specialist, West Lafayette. 

 

My son recommended only making one fungicide pass in corn this year after attending a crops conference a few months ago. When should we make that pass? Should we consider two passes if southern rust pressure was high in our area last year? 

 

Flaningam: Research shows that corn fungicide application should be done at VT to R1. Do not judge your fungicide application based upon the prior years’ disease progression. Scout those fields after the initial fungicide application, at approximately the R3 growth stage. Make a management decision on whether to apply a second fungicide based upon the hybrid’s disease tolerance, severity of disease infestation and crop growth stage. Lastly, review the weather forecast. The air temperature and humidity are key factors that can enhance disease progression.

 

Joern: One well-timed pass can be as effective as two suboptimally timed passes. Fortunately for you, southern rust does not overwinter in our area. Just because you had it bad last year doesn’t mean much as it relates to 2026. If you’re making one fungicide pass, VT/R1 is the sweet spot. University data and on‑farm trials confirm this is the most reliable ROI timing. 

 

Southern rust blows in, cycles fast and has one of the shortest latent periods of any major corn disease. That means a single VT/R1 spray might have run out of gas before rust peaked last year. In high‑risk areas for tar spot or early infection of southern rust, a VT/R1 pass and a later R3‑ish pass can be justified, but only when disease is present and spreading. Most years, one well‑timed pass is enough. Remember, the yield response to fungicide is based on your practices, locale, disease pressure and genetics.

 

Kneubuhler: A single fungicide pass in corn is typically the most profitable approach. Timing is far more important than the number of applications. The ideal window is VT to R1, when the plant is determining yield and the upper canopy contributes most to grain fill. Applications made earlier rarely provide a strong return unless disease is already present and actively spreading, which is uncommon in most years.

 

Only consider a second pass if multiple risk factors are present, such as early disease development, susceptible hybrids, continuous corn or favorable weather for disease. Even with concerns like southern rust, last year’s pressure alone isn’t enough to justify two applications. What matters is when and how severely disease shows up this season. In most cases, a well-timed VT/R1 application, combined with good scouting leading up to tassel, will provide the best return and adequate protection.

 

Quinn: Foliar fungicide applications at R1 to R2 tend to provide the most consistent and reliable disease control and yield response when disease pressure is present. Only make two passes in years where disease pressure is high and infection occurs early in the season. 

 

Multiple fungicide applications are typically only justified in fields with severe, early-developing disease pressure, especially when infection occurs up to a week or two before tasseling and weather conditions favor rapid spread. In those situations, an earlier pass may help slow disease development, with a second application at the R1 to R3 growth stage providing protection during grain fill. Without early and escalating disease pressure, a second pass rarely provides a consistent economic return. 

 

In addition, high southern rust pressure last year does not automatically mean you should plan two sprays this year. Southern rust is highly dependent on weather and wind, and its arrival and severity vary widely each season. Scout regularly and monitor regional disease forecasts. If southern rust shows up early in your region and begins moving quickly into the upper canopy before tasseling, then a two-pass fungicide system may be warranted. However, one well-timed pass (or no pass at all) is often sufficient.