Boost crop resilience through advanced disease control and sustainable soil management practices
In the stillness of a humid summer morning, danger might be quietly spreading through your cornfield. What appears as a start for a productive season can quickly take a devastating turn when tar spot strikes.
What is tar spot?
This relentless disease, caused by the fungus Phyllachora maydis, has rapidly escalated from an isolated concern to a widespread menace since its U.S. debut in 2015. Its ability to take hold and wreak havoc across acres of once-healthy corn fields has left growers scrambling for solutions that preserve prime farmland, strengthen their soil ecosystem, and sustain their operations.
Tar spot is no ordinary disease—it strikes at the heart of productivity, slashing yields by up to 50% in affected areas. For growers, this level of loss can mean the difference between a profitable harvest and a financial disaster. Even a moderate outbreak can ripple through an operation, reducing grain quality, cutting revenue, and driving up management costs.
Initially confined to Illinois and Indiana, tar spot has since spread like wildfire, infiltrating prime soil in states such as Michigan, Wisconsin, Iowa, Missouri, and beyond. As it continues its march across the Midwest, it threatens to reshape the landscape of corn production, leaving growers with little choice but to respond by enhancing soil functionality, strengthening crop defenses, and fighting the disease pressure directly through new modes of action.
Luckily, there are effective methods for combating tar spot. Keep reading to find out how innovative solutions can safeguard your yields and boost your crop’s defenses against tar spot.
Identification of corn tar spot symptoms for early disease management
Tar spot is a stealthy adversary, often starting small but eventually proving itself capable of escalating into a severe infestation. Early detection is critical, as recognizing the symptoms as soon as possible allows growers to take swift action to protect their corn crops and minimize damage.
Leaf symptoms
The first visible signs of tar spot are small, raised, black lesions or spots on the upper leaf surface. These spots, which resemble flecks of tar, might seem minor at first, but their presence marks the beginning of a serious infection. As the disease progresses, these lesions multiply and merge, creating larger necrotic areas that severely impair the plant’s ability to photosynthesize, which deprives it of the energy needed for growth and grain production. Over time, this can lead to significant yield reductions and weakened plant health that leave the crop vulnerable to additional stressors.
Stem and husk symptoms
In severe cases, tar spot doesn’t stop at the leaves. The black lesions can extend to the stems and husks, further undermining the plant’s health. This widespread infection compromises the structural integrity of the plant and increases its susceptibility to lodging during adverse weather conditions like heavy rain or high winds. Plants weakened by tar spot are also more prone to secondary infections that compound the damage and further threaten yield and quality.
Distinguishing tar spot from other diseases
Making a correct diagnosis is crucial in managing tar spot effectively. Unlike common rust or southern rust, where pustules can be wiped away, tar spot lesions cannot be scraped off the leaf surface. Recognizing this distinguishing feature simplifies the identification process for growers, who can then apply the correct treatments and take targeted measures to combat the disease.
Conditions that favor tar spot and impact soil health
Tar spot thrives in cool, humid environments, with temperatures between 60–70°F and relative humidity above 75%. These factors are most common during early- to mid-growing seasons, especially in regions with frequent rainfall or heavy morning dew. Left unchecked, such conditions can quickly turn minor infections into widespread outbreaks that threaten entire fields.
Moisture levels
Moisture is a key driver of tar spot infections. Dew, rain, or irrigation water that lingers on leaves for more than seven hours provides an ideal environment for fungal spores to germinate and infect plants. Fields with poor drainage or low-lying areas where water collects are particularly vulnerable. Improving soil drainage and optimizing irrigation practices are crucial steps to limit the disease’s spread.
Field history and residue
Fields with a history of tar spot are also at greater risk of recurring infections. The fungus overwinters in corn residue, lying dormant until conditions favor its resurgence. No-till or reduced-till systems can exacerbate this risk, as they leave more residue on the surface. Implementing strategies like crop rotation, cover crops, and post-harvest residue management can significantly reduce the inoculum load and improve soil health to disrupt the pathogen’s lifecycle and make fields less hospitable to the disease.
Economic impact of tar spot
In regions hardest hit, tar spot has been linked to yield reductions of 20 to 60 bushels per acre (or an average of 104 million bushels from 2018-2023 in the U.S.), turning promising harvests into financial setbacks. The disease’s rapid progression means that a healthy crop can deteriorate in mere weeks, leaving growers with limited time to react.
Quality deterioration
The disease doesn’t stop at reducing yields—it also compromises grain quality. Tar spot-infected kernels are often lighter, poorly filled, and visually unappealing. These defects can lead to price penalties or outright rejection in both processing and export markets. For growers dependent on premium grain prices, such losses cut deeply into profit margins.
Increased management costs
Effectively managing tar spot is also resource intensive. Fungicide treatments, often requiring multiple applications per season, come with significant costs. Coupled with increased labor for field scouting and application, these expenses place a heavy financial burden on growers, especially during high-pressure seasons.
How to fight tar spot in corn crops
Managing tar spot requires more than just reactive measures. It demands innovative, science-backed solutions that target the common pests and pathogens but also strengthen the crop’s overall health. Enter Tidal Grow® Spectra, a revolutionary product designed to transform the way growers combat tar spot and other crop stressors.
Finding the right bioactive solution for tar spot
So, what’s the best fungicide for tar spot in corn? Growers need a product that offers additional perks. Spectra is a multi-modal bioactive solution, serving as a fungicide, bactericide, and nematicide. It’s precisely bioengineered to fight diseases like tar spot while enhancing the crop’s immune system (using chitosan as its active ingredient). Unlike traditional chemical fungicides, Spectra takes a holistic approach, addressing pest and disease suppression while stimulating plant health.
The power of chitosan-based technology
The power of Spectra’s efficacy lies in its advanced chitosan-based technology. Chitosan, derived from chitin, is known for its powerful pest and pathogen control and immune-boosting properties—when formulated properly. When applied, Spectra works by inhibiting fungal growth and enhancing the plant’s natural defense mechanisms to help support abiotic stressors.
This dual-action technology provides a multi-modal approach to common pests and pathogens.
- First, Spectra disrupts the fungal cell membranes, effectively halting the pathogen’s growth.
- Simultaneously, it interferes with pathogen RNA synthesis, preventing the fungus from reproducing and spreading further.
This comprehensive mode of action makes Spectra exceptionally effective in reducing tar spot severity, even under high disease pressure.
Beyond its direct impact on tar spot, Spectra also enhances plant immunity, helping crops fend off other potential stressors. Strengthening the plant from within ensures that crops can survive and thrive in challenging conditions.
Field trial results
The real-world performance of Spectra was put to the test during the 2023 growing season in Quitman, GA. These trials were conducted under high disease pressure, providing an ideal environment to evaluate Spectra’s capabilities in combating tar spot and improving crop outcomes.
Overview of the trial
The field trials followed a rigorous randomized block design to ensure the accuracy and reliability of the results. Treatments were applied twice throughout the season to simulate typical fungicide application practices. This approach allowed researchers to compare the efficacy of Spectra tank-mixed with a standard fungicide (at half-rate) against untreated controls and full-rate fungicide-only treatments.
The trial’s conditions were intentionally challenging, with high tar spot prevalence and favorable environmental conditions for fungal growth. This ensured that the product was tested in a setting that closely mirrored the pressures faced by commercial growers.
Key results
The trial produced compelling evidence of Spectra’s effectiveness:
- Yield improvement: When Spectra was tank-mixed with a standard fungicide at half rate (0.5x), yield increased by 3% compared to untreated controls. This yield boost demonstrates Spectra’s ability to enhance the performance of standard fungicide programs while reducing chemical input.
- Reduction in disease severity: Tar spot severity was significantly reduced in plots treated with the Spectra tank mix. The accompanying chart highlights these results, showing consistently lower leaf severity percentages in Spectra-treated plots compared to untreated (UTC) and even grower-standard treatments.
As illustrated in the chart, Spectra consistently outperformed other treatments, particularly in late-season assessments when disease pressure peaked. By October, untreated plots showed over 60% leaf severity, while Spectra-treated plots maintained far lower levels of infection—less than 20%. This marked reduction in disease incidence underscores Spectra’s efficacy in managing tar spot, even under intense field conditions.
Spectra application protects corn and improves soil quality
Application rate
Timing is critical when it comes to managing tar spot. For reactionary treatment, Spectra should be applied during the mid-season growth stages, specifically between the VT (tasseling) and R1 (silking) stages (when fungicides are typically applied). This period is when tar spot symptoms are most likely to emerge, and the disease can cause the most damage if left untreated.
- The recommended application rate for Spectra ranges from 8 to 12 fl oz. per acre, depending on the severity of the disease pressure and if the grower is taking a proactive or reactive approach.
- For areas that have historically experienced moderate tar spot pressure, starting at the lower end of the rate range may be sufficient with one to three applications throughout the season, offering a proactive approach in combatting tar spot.
- However, in fields with high disease pressure or a history of severe outbreaks, growers will likely need to increase application rates and frequency.
- Contact your local agronomist for specific recommendations.
Application methods
Spectra offers flexibility in application methods, making it easy to integrate into existing crop management routines. Spectra can be tank-mixed with other fungicides to enhance overall disease control. This is particularly effective in integrated pest management (IPM) programs where multiple pathogens may pose a threat. It can be applied using the following methods:
- In-furrow application: this method places Spectra directly into the soil at planting, offering early-season protection and enhancing soil health.
- Foliar spray: As a foliar spray, Spectra provides direct protection to the leaves, targeting the primary site of tar spot infection.
Before tank-mixing Spectra with other products, it’s valuable to perform a jar test to ensure compatibility. This simple test helps prevent adverse chemical reactions that could compromise the efficacy of the tank mix or damage application equipment.
By following these application guidelines, growers can take full advantage of Spectra. Whether used as a standalone product or in combination with other fungicides, Spectra offers a powerful, flexible solution for managing tar spot among many other pests and pathogens while promoting healthier, more resilient crops.
Maximizing ROI with Spectra
One of Spectra’s greatest strengths is its ability to reduce disease-related yield losses. By controlling tar spot more effectively than conventional fungicide programs alone, Spectra helps growers defend their harvest and realize the full potential of their fields. This means higher yields even in seasons with high disease pressure that requires every acre to work harder for the grower’s bottom line.
Additionally, Spectra’s advanced chitosan-based technology can offer efficacy at lower fungicide rates, reducing overall input costs. With yield improvements of up to 3% (when tank-mixed with a standard fungicide at half rate), Spectra provides growers with a powerful tool for optimizing costs without sacrificing performance.
A “Safer Choice” for applicators and crops
We believe that growers shouldn’t compromise safety with their bioactive solutions, which is why Spectra:
- Has a non-toxic formulation: 0 PHI and 0 REI
- Does not require additional PPE for applicators
- Is listed as a 25(b) pesticide: Approved by the EPA as a minimum-risk pesticide, exempt from federal registration requirements (FIFRA 40 CFR 152)
- Is safe for crops and applicators†
†Safe when used as directed. Chitosan, the active ingredient in Spectra, was designated Safer Choice by the EPA in 2024.
Conclusion: safeguard corn yields and strengthen soil health with Spectra
Tar spot remains a formidable foe for corn growers, but with the right tools and strategies, it’s a challenge that can be effectively managed. Spectra, with its advanced bioactive technology, offers a new approach to pest and pathogen control that also enhances plant health.
Key takeaways
- Tar spot is a serious threat: As one of the most damaging diseases in corn production, tar spot can severely impact both yield and profitability. Proactive management is essential to minimize its effects.
- Add Spectra to your IPM strategy: Spectra provides growers with a tool to combat tar spot effectively while working with other active ingredients to optimize efficacy.
Don’t let tar spot compromise your harvest—reach out to a Tidal Grow AgriScience representative today to learn how Spectra can fit seamlessly into your crop management plan.
Citations
(2019, March 19). Tar Spot of Corn. Crop Protection Network. https://cropprotectionnetwork.org/encyclopedia/tar-spot-of-corn
Crop Protection Network. (2020, May 1). An overview of tar spot. Retrieved from https://cropprotectionnetwork.org/publications/an-overview-of-tar-spot
Gullickson, G. (2024, December 23). Want to preserve corn yield by more than 50%? Farm Progress. Retrieved from https://www.farmprogress.com/crop-disease/want-to-preserve-corn-yield-by-more-than-50-
(n.d.). Safer Choice. United States Environmental Protection Agency. https://www.epa.gov/saferchoice
(n.d.). Section 25(b) Exempt Pesticide Products. Department of Pesticide Regulation. https://www.cdpr.ca.gov/docs/registration/sec25/sect25intro.htm
Telenko, D., et al. (2021, March 16). Tar spot of corn web book. Crop Protection Network. Retrieved from https://cropprotectionnetwork.org/web-books/tar-spot-of-corn
