Tar spot and Southern rust proved to be quite problematic for corn growers during the 2025 season. Some reports indicate disease levels were unprecedented, resulting in 50+ bu/A yield losses in some locations. As the 2026 season approaches, weather outlooks remain uncertain—conditions across the Midwest could shift toward increased rainfall favoring disease development, or persist in dryness heightening environmental stress. Regardless of what Mother Nature delivers, there are important lessons from 2025 that can help guide growers in making informed management decisions for the upcoming season.
Tar spot: Hidden infection, visible losses
Figure 1: Spread of tar spot on corn in 2025. Dark yellow indicates counties where tar spot was confirmed. Source: Crop Protection Network. Tar Spot Map. Corn Integrated Pest Management PIPE, https://corn.ipmpipe.org/tar-spot-2025/. Accessed 04 June 2026.
Tar spot has rapidly evolved from an emerging disease to a major yield threat. By 2025, it was confirmed in at least 20 states and continued expanding across the Corn Belt (Figure 1). Yield losses reached nearly 188.8 million bushels, highlighting its economic impact.
Figure 2: 2024 colorized electron microscopy images of tar spot in corn. Tar spot spores and mycelium have been colorized in blue. Corn leaf tissue is colorized green. Photos depict how tar spot spores invade corn leaf tissue reducing photosynthetic ability before visible lesions are present. Veltyma fungicide application occurred 3 days before inoculation with tar spot (Phyllacora maydis). Plants grown in controlled conditions at 25°C, 14-hr photoperiod in a growth chamber.
Figure 3: Tar spot infected corn ear leaf. Photo taken in August 2025 in Madison County, IA.
Severe infections can drive premature senescence, limiting grain fill and, in extreme cases, leading to plant death. With documented losses of 50+ bu/A in high-pressure environments, the key lesson from 2025 is clear: tar spot must be managed proactively, not reactively.
Southern rust: Rapid spread and high yield impact
Southern rust brought a different, but equally severe, challenge in 2025. This windborne disease migrates north each season from southern regions, thriving under warm, humid conditions. Its spread across the U.S. in 2025 reached major corn-producing regions—and even extended into Canada (Figure 4).
Figure 4: Spread of Southern rust on corn in 2025. Red indicates counties where Southern rust was confirmed. Source: Crop Protection Network. Southern Rust Map. Corn Integrated Pest Management PIPE, https://corn.ipmpipe.org/southern-corn-rust-2025/. Accessed 04 June 2026.
Field symptoms include bright orange pustules on leaf surfaces, which rapidly multiply and disrupt photosynthesis (Figure 5). Unlike tar spot’s slower development, Southern rust can escalate quickly during reproductive stages, making timing of control critical.
Figure 5: Corn leaf photos infected with Southern rust (orange pustules on upper leaf surface).
The result in 2025 was significant: southern rust was the most yield-limiting corn disease, responsible for losses exceeding 517 million bushels (Figure 6). Its aggressiveness reinforces the need for early detection and timely fungicide applications.
Figure 6: 2025 BASF-sponsored large-scale demonstration trial. Houston Co., MN. Veltyma fungicide applied at VT/R1 (7/17/2025). Photo taken 40 DAT (8/26/2025). Primary disease: Southern rust. Can see to the line where Veltyma fungicide was not sprayed. Corn was subject to heavy Southern rust pressure, forcing the plants to speed up their reproductive cycles and start drying down prematurely.
2025 takeaways: Why these diseases demand attention in 2026
Tar spot and Southern rust share several characteristics that make them persistent threats:
- Disease develops before symptoms appear, due to latent period
- Weather variability—heat, moisture, and humidity—continues to favor outbreaks
- Wide geographic spread, driven by residue (tar spot) and windborne movement (Southern rust)
The main lesson from 2025 is that waiting for visible symptoms is often too late. Effective management in 2026 will require proactive, well-timed fungicide programs that protect yield potential before disease pressure peaks.
Timing matters: Veltyma® Fungicide application options
Figure 7: Veltyma fungicide offers rate and timing flexibility to help optimize yield potential on corn.
Research has shown that over time and across geographies, protecting corn as it enters its reproductive period is critical for preserving yield potential. However, during years with heavy disease pressure (like 2025), customers often wonder if they need two fungicide applications on their corn. With a performance-driven fungicide like Veltyma, there are several options to choose from. Whether growers choose a single VT application, an increased rate under high pressure, or a two-pass program for early infection/yield-pushing scenarios, the goal is the same—protect the crop before disease impact occurs (Figure 7). Consult with your local BASF representative if there are questions around optimal timings and rates.
Preparing for 2026 with Veltyma® Fungicide
Veltyma® fungicide from BASF offers a comprehensive solution built for today’s challenges. It provides broad-spectrum control of both tar spot and Southern rust, along with strong residual activity to protect corn during critical growth stages.
As we prepare for 2026, it is still unclear whether our crops will be subject to disease stress or environmental stress. Regardless of what mother nature brings, remember that what sets Veltyma fungicide apart is its ability to deliver performance beyond disease control:
- Consistent Disease Protection: Long-lasting residual control helps maintain protection even under prolonged disease pressure.
- Optimized Growth Efficiency: Improved photosynthesis, nitrogen utilization, and plant health support stronger yield potential.
- Environmental Stress Mitigation: Enhanced tolerance to heat, drought, and other stresses helps stabilize performance across varying conditions to continue driving yield.
Across multi-year, multi-state trials, Veltyma has consistently delivered yield advantages—averaging approximately +11.8 bu/A over untreated crops and + 7.0 bu/A over other brands available on the market—demonstrating reliable performance across time and geography.
Bottom line
The 2025 season reinforced that tar spot and Southern rust are not isolated threats—they are widespread, yield-limiting diseases that demand a proactive approach. As growers plan for 2026, following proven application strategies and investing in a consistent performer like Veltyma fungicide is essential to protecting both crop health and yield potential in an increasingly challenging environment.
