Evaluating Tar Spot Management Strategies
In recent years, tar spot has expanded its footprint, becoming a persistent challenge for farmers across the U.S. The disease has long been a problem in South and Central America but has progressively moved northward in the past decade. Early on, there were questions as to whether it would be able to overwinter in the cooler climate of North America, but it seems those speculations have been put to rest, and the answer is not what U.S. producers were hoping for. However, each year brings new insights, and with that, we’re gaining better knowledge of the disease’s biological characteristics and evolution, which can help us dial in on the most effective management strategies.
Unlike some diseases, such as southern rust, which depend on windborne spores traveling through the jet stream, recent findings suggest that tar spot can overwinter in most U.S. soils. This makes the disease a significant annual threat, especially for northern producers. Studies indicate that up to 25% of spores may remain viable in springtime, making it a recurring problem from one year to the next.2 The disease’s ability to thrive under diverse climatic conditions – ranging from high humidity to moderate rainfall – also complicates prediction models and management programs.
The best time to apply a fungicide for tar spot management typically occurs during the early reproductive stages, between tasseling and the R2 growth stage. In areas with high disease pressure, some farmers are even exploring multiple fungicide applications. While this approach increases costs, it may be necessary to protect high-yield-potential fields.
To be effective against tar spot, fungicides must contain active ingredients from at least two of the following FRAC groups: 3, 7 or 11. Ideally, a fungicide will include actives from all three groups to ensure comprehensive protection and prolong resistance. Consult with your trusted agronomic advisor to select fungicides tailored to your specific conditions and hybrid selections.
**Strategy effectiveness rating: High. Fungicides are typically the best current defense against tar spot.
Try to prioritize hybrids with strong disease tolerance in fields with lower yield potential where a foliar fungicide application may not be an attractive option. This ensures some level of protection even if fungicide applications are not financially feasible on these acres. Your local WinField United retailer has access to response-to-fungicide data for CROPLAN® and partner brand seed corn hybrids, which can help you position the best products for these scenarios.
**Strategy effectiveness rating: Medium. Hybrid selection can provide limited protection against tar spot in situations where a fungicide may not be possible or economical. Also, know that many hybrids with low tar spot resistance can still provide superior yields when treated with a fungicide or if tar spot is absent, so selecting only on this basis may hinder overall profitability.
Predictive tools developed by universities attempt to assess tar spot risk levels based on climatic factors such as rainfall, temperature, and humidity; however, these tools are not infallible, and accuracy is highly variable. This uncertainty forces farmers to gamble on fungicide applications, weighing the potential cost against the risk of significant yield losses. Waiting to see if conditions are right for disease development may not provide enough time to coordinate treatment with aerial applicators, so it’s always best to plan a preventative application ahead of the season to avoid missing critical timing windows.
**Strategy effectiveness rating: Low. The current predictive tools may not always provide accurate risk assessments and probably aren’t localized enough with the data they use to make their prediction.
**Strategy effectiveness rating: Low. Spore viability in the soil is still being researched so it’s unclear whether these strategies would actually reduce infections or just prolong them until the field is put back into corn.
The Advanced Acre® Rx (AARx) program was built to help farmers manage tough decisions like those associated with tar spot. AARx can help mitigate the financial risks tethered to fungicide applications that may not deliver sufficient ROIs. While fungicides are still not guaranteed to pay off every year, tar spot's growing prevalence and impact have made their use increasingly more justifiable. AARx helps make the decision easier by providing a service warranty if certain yield thresholds aren’t met.*
1 Tar Spot: An Understudied Disease Threatening Corn Production in the Americas
Valle-Torres J, Ross TJ, Plewa D, et al. 2020. Plant Disease. 104:10, 2541-2550.
2 Groves C, Kleczewski N, Telenko D, et al. Phyllachora maydis Ascospore Release and Germination from Overwintered Corn Residue. 2020. Plant Health Progress.
*Agreement is required and conditions, restrictions and service fees apply. Percentage goals for the Approved Yield range from 95–105% for corn and 95–100% for soybeans. Due to factors outside of WinField United’s control, results to be obtained cannot be predicted or guaranteed by WinField United. Results may vary.
All photos are either the property of WinField United or used with permission.
© 2025 WinField United. Important: Before use always read and follow label instructions. Crop performance is dependent on several factors many of which are beyond the control of WinField United, including without limitation, soil type, pest pressures, agronomic practices and weather conditions. Growers are encouraged to consider data from multiple locations, over multiple years and to be mindful of how such agronomic conditions could impact results. Advanced Acre, CROPLAN and WinField are trademarks of WinField United. All other trademarks are the property of their respective owners.
Why Does Tar Spot Management Matter?
Tar spot is a fungal disease that affects corn, causing black, tar-like spots on leaves, which can reduce the plant’s photosynthetic capacity and steal resources the plant would otherwise use to fuel growth and reproduction. In severe cases, it can lead to significant yield losses of up to 30%.1 On a 200-bushel-per-acre corn field, this can translate to a staggering 60-bushel loss, or nearly a third of a farmer’s income potential on that acre. Beyond direct yield losses, tar spot also seems to decrease the plant’s natural defense mechanisms, which it relies on to fight off infections from various stalk and crown rot pathogens. This can result in compromised standability and a more challenging harvest.Unlike some diseases, such as southern rust, which depend on windborne spores traveling through the jet stream, recent findings suggest that tar spot can overwinter in most U.S. soils. This makes the disease a significant annual threat, especially for northern producers. Studies indicate that up to 25% of spores may remain viable in springtime, making it a recurring problem from one year to the next.2 The disease’s ability to thrive under diverse climatic conditions – ranging from high humidity to moderate rainfall – also complicates prediction models and management programs.
Tar Spot Management Strategies
Historically, farmers have used several cultural and/or chemical strategies to anticipate and manage fungal diseases. Based on our latest information, here’s a breakdown of what is and is not effective when it comes to controlling tar spot.Fungicides
Given tar spot’s persistence and destructive potential, fungicides have emerged as the primary line of defense to protect yield. Until recent years, the return on investment (ROI) for foliar fungicides has lacked consistency, particularly in the northern geographies; however, tar spot has changed this dynamic, making fungicide applications a more reliable and necessary investment across most regions in the U.S.The best time to apply a fungicide for tar spot management typically occurs during the early reproductive stages, between tasseling and the R2 growth stage. In areas with high disease pressure, some farmers are even exploring multiple fungicide applications. While this approach increases costs, it may be necessary to protect high-yield-potential fields.
To be effective against tar spot, fungicides must contain active ingredients from at least two of the following FRAC groups: 3, 7 or 11. Ideally, a fungicide will include actives from all three groups to ensure comprehensive protection and prolong resistance. Consult with your trusted agronomic advisor to select fungicides tailored to your specific conditions and hybrid selections.
**Strategy effectiveness rating: High. Fungicides are typically the best current defense against tar spot.
Hybrid Selection
You can also mitigate tar spot risk through careful hybrid selection. While no hybrids offer complete resistance, some have demonstrated better tolerance to the disease. Plant breeders are actively working to identify and incorporate resistance genes into new hybrids, but this process is complex due to the unique biology of tar spot.Try to prioritize hybrids with strong disease tolerance in fields with lower yield potential where a foliar fungicide application may not be an attractive option. This ensures some level of protection even if fungicide applications are not financially feasible on these acres. Your local WinField United retailer has access to response-to-fungicide data for CROPLAN® and partner brand seed corn hybrids, which can help you position the best products for these scenarios.
**Strategy effectiveness rating: Medium. Hybrid selection can provide limited protection against tar spot in situations where a fungicide may not be possible or economical. Also, know that many hybrids with low tar spot resistance can still provide superior yields when treated with a fungicide or if tar spot is absent, so selecting only on this basis may hinder overall profitability.
Scouting and Predictive Tools
One of the challenges of managing tar spot is that by the time visible symptoms appear, the pathogen has already inflicted damage. Scouting, therefore, offers limited utility for reactive management. While some fungicides have limited curative properties, their effectiveness is still reduced once the disease is established.Predictive tools developed by universities attempt to assess tar spot risk levels based on climatic factors such as rainfall, temperature, and humidity; however, these tools are not infallible, and accuracy is highly variable. This uncertainty forces farmers to gamble on fungicide applications, weighing the potential cost against the risk of significant yield losses. Waiting to see if conditions are right for disease development may not provide enough time to coordinate treatment with aerial applicators, so it’s always best to plan a preventative application ahead of the season to avoid missing critical timing windows.
**Strategy effectiveness rating: Low. The current predictive tools may not always provide accurate risk assessments and probably aren’t localized enough with the data they use to make their prediction.
Cultural Practices and Residue Management
Cultural practices like crop rotation and residue management have limited effectiveness against tar spot. While burying residue may temporarily reduce spore loads, future tillage eventually brings them back to the surface, and the longevity of survival of these spores in the soil is still not very well understood. Furthermore, tar spot spores can travel significant distances in the wind so even fields with low local spore numbers are vulnerable to infections from neighboring farms.**Strategy effectiveness rating: Low. Spore viability in the soil is still being researched so it’s unclear whether these strategies would actually reduce infections or just prolong them until the field is put back into corn.
Economic Considerations
Farming is always difficult, but tight margins make management decisions increasingly more strenuous. If applying fungicides across all of your acres isn’t financially feasible, consider prioritizing high-yield potential fields for treatment to improve ROI potential on these acres. Lower-productivity fields where other stresses are often a more significant factor than fungal pathogens might be better managed with disease-tolerant hybrids than fungicides. Your local agronomist can help you make these determinations.The Advanced Acre® Rx (AARx) program was built to help farmers manage tough decisions like those associated with tar spot. AARx can help mitigate the financial risks tethered to fungicide applications that may not deliver sufficient ROIs. While fungicides are still not guaranteed to pay off every year, tar spot's growing prevalence and impact have made their use increasingly more justifiable. AARx helps make the decision easier by providing a service warranty if certain yield thresholds aren’t met.*
Planning for Tar Spot This Season
Tar spot appears to be here to stay, and its management requires a proactive approach. When you balance fungicide use, hybrid selection and economic realities, you’ll be in a strong position to maximize your profitability potential. Contact your WinField United retailer to stay up to date on the latest tar spot management recommendations and get the best local seed recommendations for your area.1 Tar Spot: An Understudied Disease Threatening Corn Production in the Americas
Valle-Torres J, Ross TJ, Plewa D, et al. 2020. Plant Disease. 104:10, 2541-2550.
2 Groves C, Kleczewski N, Telenko D, et al. Phyllachora maydis Ascospore Release and Germination from Overwintered Corn Residue. 2020. Plant Health Progress.
*Agreement is required and conditions, restrictions and service fees apply. Percentage goals for the Approved Yield range from 95–105% for corn and 95–100% for soybeans. Due to factors outside of WinField United’s control, results to be obtained cannot be predicted or guaranteed by WinField United. Results may vary.
All photos are either the property of WinField United or used with permission.
© 2025 WinField United. Important: Before use always read and follow label instructions. Crop performance is dependent on several factors many of which are beyond the control of WinField United, including without limitation, soil type, pest pressures, agronomic practices and weather conditions. Growers are encouraged to consider data from multiple locations, over multiple years and to be mindful of how such agronomic conditions could impact results. Advanced Acre, CROPLAN and WinField are trademarks of WinField United. All other trademarks are the property of their respective owners.
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