What the research measured
The cited 2014–15 meta-analysis across 13 states and Ontario reported a mean corn yield response of 332.9 kg/ha (about 5.3 bu/ac) to a foliar fungicide, with 68.2% of 436 treatment-studies positive and the VT timing 2.9 times the V6 response. The earlier 2002–09 meta-analysis reported mean gains of 230 to 390 kg/ha (about 3.7 to 6.2 bu/ac) by product. Under high tar spot severity in Indiana the average gain was 14.6 bu/A; under low severity it was −2.7 bu/A, and Iowa State detected no yield effect at any of six 2022 locations.
Two multi-state meta-analyses of uniform university trials (2002–09, 14 states; 2014–15, 13 states and Ontario), a Crop Protection Network summary of 2019–21 multi-state tar spot trials, Iowa State’s six-location 2022 program and a single 2024 Purdue planting-date trial.5 independent sources.What it is. A single foliar pass of a strobilurin (QoI), triazole (DMI) or SDHI fungicide, usually a premix of two or three of them, sprayed at tassel to silking (VT/R1) to protect the ear leaf and canopy from tar spot, gray leaf spot and other late-season leaf diseases. Ground or aerial application; Trivapro at 13.7 fl oz/A was the product in the Indiana timing experiments cited here.
Study conditions and limitations
- Response tracks disease: the Indiana tar spot study averaged +14.6 bu/A (range 6.2 to 22.2) under high severity and −2.7 bu/A (range −11.9 to 9.3) under low severity, where the partial net return ran from a $46.5 loss to a $5.8/A loss.
- Iowa State’s 2022 trials at six research farms detected no effect of any fungicide on yield (P>0.1), even though V12 and R1 applications reduced tar spot and gray leaf spot; non-sprayed check yields ran from 178.6 to 250.5 bu/ac and tar spot reached 23.2% in the Crawfordsville check.
- At low disease (<5% severity) the 2002–09 analysis put the probability of not recovering a $40–95/ha application at 0.55–0.98 for pyraclostrobin and 0.91–0.99 for azoxystrobin at $0.12/kg corn; above 5% severity the range was 0.25–0.69 for propiconazole + trifloxystrobin and 0.37–0.98 for azoxystrobin.
- Timing matters: the 2014–15 analysis found VT (376.8 kg/ha) and V6 + VT (493.9 kg/ha) responses well above V6 alone (127.4 kg/ha), and an R5 application in Indiana gave the smallest tar spot reduction (13%).
- Mode-of-action count matters: DMI + SDHI + QoI premixes averaged 574.4 kg/ha against 180.5 kg/ha for a solo QoI, DMI alone gave no substantial response, and the tar spot trials found two- or three-MOA products suppressed disease more than one.
- The 7–18 bu/A protection in Purdue’s 2024 trial came from one northern Indiana site and was significant only at the earlier of two planting dates.
Read the sources · 5
- Meta-analysis of yield response of foliar fungicide-treated hybrid corn in the United States and Ontario, Canada ↗
Uniform trials in 13 states and Ontario in 2014–15: 68.2% of 436 treatment-studies had a positive yield response and the overall mean was 332.9 ± 29.1 kg/ha (about 5.3 bu/ac). VT applications (376.8 kg/ha) returned 2.9 times the V6 response (127.4 kg/ha); DMI + SDHI + QoI premixes gave 574.4 kg/ha, DMI + QoI 390.8 and QoI alone 180.5.
- Meta-analysis of yield response of hybrid field corn to foliar fungicides in the U.S. Corn Belt ↗
University trials in 14 states, 2002–09: mean yield gains of 390 kg/ha for propiconazole + trifloxystrobin, 331 for propiconazole + azoxystrobin, 256 for pyraclostrobin and 230 for azoxystrobin, all significant but highly variable. At $0.12/kg corn and $40–95/ha costs, the probability of not recovering the cost was 0.55–0.99 when disease severity was under 5%.
- Multi-state fungicide efficacy trials to manage tar spot and improve economic returns in corn in the U.S. and Canada ↗
Small-plot trials in 2019–21 in Illinois, Indiana, Michigan, Wisconsin and Ontario: yield protection from a VT/R1 fungicide ranged from 1.5 to 7.9% under low to moderate tar spot and 3.1 to 8.5% under high severity. In the Indiana timing experiments (Wanatah and West Lafayette, Trivapro) the average gain was 14.6 bu/A (6.2–22.2) under high severity and −2.7 bu/A (−11.9 to 9.3) under low severity.
- 2022 Summary of Foliar Fungicide Applications on Corn in Iowa ↗
Six Iowa research farms, six replications, seven products at V12 and eight at R1: no effect of any fungicide on yield at any location (P>0.1). Non-sprayed check yields ran from 178.6 to 250.5 bu/ac; V12 and R1 applications reduced tar spot and gray leaf spot (P<0.1), while planting or V6 applications had little effect.
- Tar Spot: What To Look For In Corn And Making An Informed Decision On Fungicide Application ↗
In a single 2024 trial at the Pinney Purdue Ag Center in northern Indiana, a VT/R1 fungicide gave 7–18 bu/A yield protection over the nontreated and significantly raised yield only in the first of two planting dates; tar spot did not reach the ear leaf until July 25.
Before you buy, ask
- What disease pressure did the trials with a yield response have, and do my fields see it?
- What application timing and rate did the cited studies use?
- Is there a scouting threshold that would tell me whether to apply this season?
Record
- Sources checked
- October 12, 2026. Every figure shown is printed on the linked page; unit conversions are noted on the chart.
- Company response
- None yet. Makers and suppliers of this product can send corrections, additional trials, or a statement; it is published here, labelled, and never edits the research summary. Send a correction →