Progress report for ONC24-142
Project Information
Unnecessary fungicide applications affect our ability to sustainably manage crop diseases. They provide opportunity for fungal pathogens to develop fungicide resistance due to routine chemical exposures. We need to conserve our use of fungicides now, so that products are available in the future as disease pressure is predicted to increase with a changing climate. Loss of fungicides will increase our reliance on techniques like tillage to bury diseased crop residue.
The recent emergence of two corn diseases in the north central US has led to even more concern about stewardship of fungicides. Tar spot and southern rust of corn can reduce yields by 45 to 50 bushels per acre in certain conditions. In 2023, some farmers in northwest Missouri chose to make three fungicide applications to manage tar spot. Success of those applications in protecting yield remains unknown. The general lack of information to assist these farmers and others in making application decisions can be addressed through on-farm strip trials.
The proposed partnership will allow University of Missouri Extension Specialists and Missouri farmers to compare single and multiple fungicide applications to corn. Reducing unnecessary fungicide use is an important component of sustainable integrated disease management.
We plan to carry out on-farm strip trials to provide information on economic and sustainability benefits (and costs) of multiple fungicide applications to corn. We will utilize the following types of data for this analysis:
- Agronomic input data like seeding rate, row spacing, irrigation, total number of active ingredients in products, growth stage at application
- Economic input costs for products and application
- Environmental data, such as topography and weather
- Yield data
Findings generated from this study will be applicable to farmers and agriculture professionals in the north central region and to technical audiences working to find sustainable disease management solutions.
Cooperators
- - Technical Advisor (Researcher)
Research
During the summer of 2024, 12 trials were initiated in Missouri cornfields across 10 counties, including five trials in fields near the Mississippi or Missouri Rivers and seven trials on non-irrigated farmland without nearby major rivers. One trial was excluded due to the inability to schedule an airplane or helicopter for the VT/R1 fungicide application, and yield data from a second trial was lost due to GPS interference caused by the aurora borealis at harvest.
For the ten trials that were successfully implemented, a fungicide application was made at the tasseling/silking growth stage (VT/R1), with the product selected by the farmer. A second application was made according to the farmer’s preferred timing and product. One farmer opted for an earlier application near the V5 growth stage, while the remaining farmers chose a second application at 3 to 4 weeks after the VT/R1 application.
The second fungicide application was applied using either strips or a randomized complete block design, depending on equipment and field size. All late applications were applied with a drone at 2 GPA that was flown approximately 11' above the canopy. The treated strips or blocks ranged in width from 40 to 120 feet, with the size determined by the field layout and the combine header width. The length of the strips or blocks ranged from 300 to 500 feet, also dependent on field size. Each trial consisted of 5 to 7 replicates, based on field size.
Strips or blocks were designed in advance, taking into account field topography, nearby buildings, and historically high and low-yielding areas to minimize the effect of field variation on the results. In-season disease rating data were collected for eight trials. However, due to an unexpected labor shortage and the rapid growth of corn in 2023, disease data could not be collected for one trial. Despite this, yield data were still obtained for all 10 trials.
Preliminary findings from year 1:
Disease Severity
Disease severity was assessed by rating the percentage of leaf area covered by disease on five plants per strip, with a minimum of 25 plants rated for the 1-pass applications and 25 plants for the 2-pass fungicide applications. The ratings focused on the ear leaf, one leaf above the ear leaf, and two leaves above the ear leaf with specific focus on southern rust and tar spot diseases. The average severity of the three leaves was calculated. Ratings were taken at the R4 to R5 growth stage, and comparisons were made between 1-pass and 2-pass treatments.
At locations where the first application was made at VT/R1 and the second application was made later, disease severity was statistically lower in the 2-pass fungicide treatment (1.1% severity) compared to the 1-pass treatments (3.1%). However, these percentages are considered low for disease severity. At one location, disease severity exceeded 5%, which is considered high. The 2-pass fungicide application corresponded to 1.2% disease severity compared to the 1-pass application at 11.3%.
At one location, the farmer opted to apply the strip treatment prior to tasseling, at the V4/V5 growth stage. In this case, disease severity in the 2-pass strips was 2%, which was statistically lower than the 1-pass application, which had 4.5% severity.
Lodging
Minimal lodging was observed in both treatments at all locations, with 10 plants per plot rated (50 plants per treatment). The results were similar for both the 1-pass and 2-pass applications. Although we did not conduct "stay green" ratings, a drone image from one field showed visible differences between treatments. Areas receiving the second fungicide application appeared less brown, indicating healthier plants compared to areas receiving a single application. We did not observe this difference in drone imagery from other locations.
Yield
Yields generally trended higher in the 2-pass treatments compared to the 1-pass treatments, with differences ranging from 1 to 3 bushels per acre, depending on disease severity. However, these differences were not statistically significant and were not sufficient to offset the cost of the additional chemical application.
Educational & Outreach Activities
Participation Summary:
Over the winter of 2024-2025, I presented preliminary findings from this work at the MU Crop Management Conference, Illinois Certified Crop Advisors Conference, and several winter meetings throughout Missouri.
Learning Outcomes
Survey feedback at winter meetings and the Crop Management Conferences indicates that farmers would reconsider their approaches to managing tar spot, specifically, as it relates to tar spot of corn.