Severe cases of tar spot in corn can kill plants and result in grain yield losses up to 60 bushels per acre.¹
How can something as simple as residue management help you mitigate the impact of this yield wrecker? Learn how these critical residue-management tactics can help you combat tar spot in corn and protect your yield.
How residue affects tar spot in corn
Caused by the fungus Phyllachora maydis, tar spot overwinters in infected residue. Spores can have up to 25% viability after overwintering in Midwest U.S. fields.
As warm, wet conditions return in the spring, wind and rain splash can transfer spores from infected residue to new corn plants. After initial infection, new tar spot lesions continually produce more spores, leading to secondary infections.
Corn residue management practices to combat tar spot in corn
Because corn residue acts as the host for tar spot over winter, something as simple as reducing infested corn residue can subsequently help reduce the amount of tar spot in your field.
While you’re at it, residue management can also help control the spread of similar diseases such as gray leaf spot and northern corn leaf blight that also overwinter in corn stubble.
The following residue-management practices can help reduce the prevalence of tar spot.
Tillage to reduce tar spot in corn
Reduced or no-till fields are often at greater risk for disease development, including tar spot infection. Tillage can help quicken the decomposition of crop residue, with deep tillage effectively burying infested corn residue and reducing fungal spore movement.²
Crop rotation to combat tar spot in corn
The most severe tar spot infections are typically found in continuous corn cropping systems due to the remaining corn residue. However, tar spot can still infect first-year corn via wind-blown spores, though these infections are typically not as severe as those from continuous corn residue.
If it is practical in your operation, rotating from corn to soybeans can allow further breakdown of infested corn residue between corn crops. Soybeans cannot host Phyllachora maydis, the fungus responsible for tar spot infections, so corn and soybean rotations can help break the disease cycle.
Foliar fungicide for tar spot in corn
If the weather cooperates, applying fungicide between VT/R1 to R3 corn growth stages will usually be most effective. Early applications typically have minimal ability to suppress tar spot.
Midwestern university researchers have found Veltyma® fungicide to be one of the most effective foliar fungicides for control of tar spot when applied at VT to R1 growth stage. With heavy disease pressure a follow up application 14 days later has shown to improve control by expanding the window of protection from this late developing disease.
Corn hybrid selection
Build a solid defense from the start by selecting corn hybrids that have been tested and rated well to withstand tar spot. Evaluate local hybrid trials and consult your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative to find the best hybrids for your area.
Crop residue management may not be a novel concept, but when executed properly, it can be a game changer for controlling tar spot in corn.
New solutions may be on the horizon by way of biological control research that is being conducted by the ARS National Center for Agricultural Utilization Research. Researchers have found that certain fungi and bacteria actually parasitize the tar spot fungus, resulting in failure of tar spot spores. Though still in its infancy, this research indicates there may be potential to biologically control tar spot in commercial fields in the future.³
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Endnotes
- Suszkiw, Jan. “Microbial Allies May Help Turn Tables on Tar Spot Fungus in Corn: USDA ARS.” U.S. Department of Agriculture, 1 Oct. 2024, www.ars.usda.gov/news-events/news/research-news/2023/microbial-allies-may-help-turn-tables-on-tar-spot-fungus-in-corn/. Accessed 2 Mar. 2025.
- Quinn, Dan, and Darcy Telenko. “Tar Spot Of Corn: What To Know And New Research.” Pest&Crop Newsletter, Purdue University, 14 June 2022, extension.entm.purdue.edu/newsletters/pestandcrop/article/tar-spot-of-corn-what-to-know-and-new-research/. Accessed 2 Mar. 2025.
- Suszkiw. “Microbial Allies May Help Turn Tables on Tar Spot Fungus in Corn: USDA ARS”
