Fungicide ROI in Corn - Timing Matters for Profit

By Blake Jackson

Growers planning fungicide applications this season should take a closer look at whether the investment will truly pay off, advises University of Missouri Extension state plant pathologist Mandy Bish.

“We have a habit of assuming ‘yield increase’ and ‘return on investment’ are interchangeable,” says Bish. “That is not always the case.” She explains that in years with minimal disease pressure, the cost of fungicide application can exceed any potential yield gains.

As of early March 2026, Missouri cash bids for No. 2 yellow corn are near $4 per bushel, making input decisions even more critical. Bish emphasizes that timing plays a major role in determining whether fungicide use will be profitable.

Corn growers also face a management challenge when balancing tar spot and southern rust. Tar spot has been detected in Missouri as early as June in recent years, but Bish cautions against reacting too quickly. The disease thrives in mild temperatures between 64-73°F and tends to slow during the hotter conditions of July.

Conversely, those same summer conditions can encourage southern rust, especially when moisture is present. “If we spray too early for tar spot, we risk having no residual protection if southern rust moves into the area,” says Bish.

Research shows the best return typically comes from a single fungicide application between VT/R1 and R3 growth stages. Studies suggest growers must prevent at least 7.5 bushels per acre in losses to break even, increasing to 15 bushels if a second application is made.

For soybeans, the return is often even less certain. “Across 66 on-farm strip trials, the average yield increase following a fungicide application was 1.8 bushels per acre,” Bish notes “Realistically, with current prices, a grower needs to see more than 3 bushels per acre to approach a positive ROI.”

Bish encourages farmers to evaluate results on their own farms. “I want farmers to confirm they are seeing the yield bump they believe they are getting,” Bish says. “Remember to factor in labor. Even if you aren’t paying someone else to spray, your time has a clear cost.”

FAQs 

• Why is ROI important for fungicide use?

It ensures the cost of application is justified by profit gains.

• What corn price is influencing decisions?

Around $4 per bushel in Missouri as of March 2026.

• When is the best time to spray corn?

Between VT/R1 and R3 growth stages.

• What is the risk of early spraying?

Loss of protection if southern rust appears later.

• What should growers do before applying fungicides?

Test their own fields and evaluate actual returns.

Photo Credit: gettyimages-oticki