Understanding The Corn Fungicide Yield Response

By Vicky Boyd

Following the advent of tar spot in the mid-2010s, fungicide applications to Midwestern corn have more than doubled from 2010 to 2021 nationally. While producers frequently have seen yield bumps from fungicides, depending on application timing, product, and disease pressure, little information was known about the mechanisms behind the response.

To bridge the knowledge gap, Purdue University Extension Corn Specialist Daniel Quinn led a two-year research project that compared an untreated check to a subsurface-banded fungicide application or a foliar fungicide application at R1. As part of the multi-location study, the team measured the effects of fungicides on leaf disease severity, grain fill duration, final kernel weight, and ultimately yields.

In addition to answering scientific questions, Quinn says the results also should be meaningful to growers. 

“This gets growers to realize there’s still quite a bit of yield to be made later in the season,” says Quinn, who along with co-authors Malena Bartaburu, Lia Olmedo Pico, and Darcy Telenko, published the research in the September–October 2025 issue of Crop Science. 

One reason why this type of research has rarely been conducted is because of the tedious plant tagging and sampling involved, he says. 

“Sometimes we had to conduct sampling every week and be careful how we sampled the kernels,” says Quinn, who is also an assistant agronomy professor at Purdue. “People have done this before with nitrogen and temperatures. It seemed like we thought we were seeing similar responses with fungicides, but we also were diving into the why, and it was trickier doing that.”

The methodology used in the studied was developed by co-author Pico during her Ph.D. studies that examined the effects of various nitrogen levels on corn kernel weight and grain fill.

Putting fungicides to the test

The studies were conducted during 2022 and 2023 at three locations within Indiana. At each site in both years, the researchers planted the same hybrid that was popular with area growers. They established small-plot trials at the Agronomy Center for Research and Education, or ACRE, in West Lafayette. There they only sampled corn kernel dry matter accumulation and duration due to data collection intensity and time constraints.

At the Northeast Purdue Agriculture Center (NEPAC) in ColumbiaCity and the Southeast Purdue Agricultural Center (SEPAC) in Butlerville, the researchers established field-scale trials. From those, they collected harvest kernel numbers, kernel weight, grain moisture, and yield data.

All of the trials included an untreated control; an at-planting treatment of flutriafol (Xyway LFR) banded about 2 inches to the side and below the seed; and a foliar application of a prothioconazole, trifloxystrobin, and fluopyram premix (Delaro Complete) at R1 or silk emergence.