6 Keys to Managing Tar Spot in Corn
October 6, 2026 Tar spot has moved from an emerging concern to a disease-management consideration for corn growers across parts of the U.S. Caused by the fungus Phyllachora maydis, the disease can reduce photosynthetic capacity and, under severe conditions, contribute to yield and grain-quality losses.
For ag retailers working with growers in areas where tar spot is present, a proactive management strategy can make a difference. Here are six keys to consider.
1. Know the field history
Tar spot management starts before the crop goes in the ground. The pathogen can survive in infected corn residue, making fields with a history of the disease important candidates for closer monitoring. Encourage growers to keep track of fields where tar spot has appeared and consider that history when developing management plans.
2. Scout early and often
Once tar spot becomes established, managing the disease becomes more challenging. Regular scouting can help identify the disease before it becomes widespread. Look for the small, raised black spots that give the disease its name, as well as surrounding tan or brown tissue that can develop with more severe infections.
3. Pay attention to weather
Environmental conditions can play a major role in tar spot development and spread. Extended periods of moisture, humidity and moderate temperatures can create favorable conditions for infection. Weather patterns, field conditions and regional disease reports can help retailers determine which fields warrant increased attention.
4. Choose hybrids with disease tolerance in mind
Hybrid selection is one of the foundational tools in an integrated tar spot management program. Encourage growers to consider the disease history of individual fields when making hybrid decisions and to evaluate available varieties for their relative level of tolerance or resistance to tar spot.
5. Get fungicide timing right
Fungicides can be an important tool when conditions and disease risk warrant treatment. However, timing matters. Applications generally work best when made preventatively or early in disease development rather than waiting until severe symptoms are widespread. Product selection, application timing and the expected disease pressure should all be considered together.
6. Build a program, not a single solution
Tar spot is unlikely to be managed effectively through one decision alone. Field history, hybrid selection, scouting, weather conditions, residue management and fungicide applications can all play a role. For retailers, bringing these pieces together creates an opportunity to help growers move from reacting to visible disease toward a more proactive management strategy.
Tar spot may continue to present new challenges as its range expands and environmental conditions vary from season to season. For ag retailers, keeping growers focused on early detection and integrated management can help put them in a better position to protect yield potential when disease pressure develops.
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