Should I Be Concerned About Tar Spot?

January 18, 2021

Tar spot was first confirmed in the U.S. corn crop during the summer of 2015 (Figure 1).¹ Curiosity turned to concern during the 2018 growing season as favorable environmental conditions (cool/wet) persisted throughout the late summer months. Considerable yield loss occurred in some Corn Belt areas in 2018 because tar spot inoculum was present and the environment favored early disease development.1 Throughout most of the Midwest in 2020, tar spot was not a factor. Why? What should be expected for 2021? Let’s discuss.

What do we know?

  • Tar spot can overwinter on corn residue in the northern U.S.
  • Spores can spread via wind and rain.
  • Tar spot favors cool, wet and humid conditions.¹
  • Certain corn products can be more resistant or susceptible to the disease.
  • Delaro® 325 SC fungicide and newly approved Delaro® Complete fungicide are labeled for tar spot control.
  • Considerable yield loss can occur given the right conditions.

Why Does This Matter?

  • Fields with higher amounts of corn residue could be at a higher risk for early infection.
  • Regardless of prior disease presence, tar spot can spread and travel rapidly given the right environmental conditions.
  • Scouting and early identification of infection is critical.
  • Fungicide is a viable option to help with control.

In summary, tar spot incidence and severity were low throughout 2020 in most of the upper Midwest due to dry and warm conditions. We continue to monitor and learn more about tar spot every year to provide better tools, products and resources for our customers. Work with your local Seedsman and agronomist on product selection and best management practices to successfully manage tar spot this next growing season and beyond.

Zak Swanson



¹Kleczewski, N. M., Chilvers, M., Mueller, D. S., Plewa, D., Robertson, A. E., Smith, D. L., and Telenko, D. E. 2019. Corn disease management: Tar spot. Tar spot. Crop Protection Network. CPN 2012-W. https://extension.purdue.edu/.

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

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