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Take Control of Tar Spot in Corn

Tar Spot is a relatively new fungal disease facing corn growers in the Midwest.

What is Tar Spot?

In 2021, Tar Spot cost U.S. corn
farmers 231.3 million bushels.1

Tar Spot can affect corn yield by
up to 60 bushels per acre.

A latency period of up to 14 days
makes it a challenge to control.

Spotting Tar Spot in Corn

  • Tar Spot has been reported in Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, Nebraska, New York, Pennsylvania and Wisconsin.
  • Spread by wind and machinery, Tar Spot reduces the plant’s ability to take in sunlight.
  • Tar Spot lesions are black spots that have a raised, bumpy texture and do not rub off.
  • The disease begins on the lower leaves and then moves to the upper plant and ear husks.

Controlling Tar Spot

Controlling Tar Spot in corn requires a multifaceted approach.

Select the Right NK Corn Hybrid


Strong Agronomics with High Yield Potential

  • Improved plant health with better roots and stalks
  • Excellent choice for higher-managed acres
  • Strong adaptation for the Central to Eastern Corn Belt

View Product Details


Excellent Yield Potential with Strong Roots and Stalks

  • Outstanding emergence for an early planting option
  • Leading drought tolerance powered by Artesian technology
  • Semi-determinate ear type and strong standability support higher populations for maximum yield potential

View Product Details


Consistent Yield Potential and Agronomics Across Environments

  • Attractive plant height and ear placement
  • Improved test weight and grain quality
  • Dependable drought tolerance

View NK1188-D Details

View NK1188-AA Details


Strong Agronomics with Good Grain Quality

  • Improved plant integrity with better roots and stalks for this maturity group
  • Good choice for higher-managed acres in the Central to Eastern Corn Belt
  • Tall and leafy hybrid for dual-purpose silage potential

View Product Details

To find the right NK corn hybrid for your fields, contact your local retailer.

Apply Fungicide When Needed

  • Early fungicide applications, at or before the first signs of development, have been effective against Tar Spot.
  • If conditions are favorable for Tar Spot development early in the season, consider a two-pass fungicide program.
  • Be sure to use multiple active ingredients.

Consider Crop Rotation and Tillage

  • Rotating to crops other than corn and using tillage to bury residue can help reduce fungus inoculum levels.

Don’t Let Tiny Spots Spell Big Problems

Download Infographic

Tar Spot FAQs

Tar Spot in corn is a new and emerging fungal disease in the Midwestern U.S. caused by Phyllachora maydis. This is not the same disease that affects maple trees, which is caused by Rhytisma acerinum.

Yes, it is a fungal disease of corn that infects and damages the upper and lower leaf surfaces of the plant. When severe, it can appear on husks and leaf sheaths as well.

Tar Spot can be identified on corn leaves by small, raised black circular spots that resemble tar and do not rub off. But in most cases, the plant is infected long before symptoms are visible.

According to the Crop Protection Network , yield losses due to tar spot can be variable, depending on the time of disease onset, weather conditions and hybrid susceptibility. In severe cases, losses of 50 bushels per acre or more have been observed on susceptible hybrids.

Yield losses are a function of reduced ear weight, poor kernel fill and vivparity (a condition in which the seed germinates while still on the cob).

Stalk rot and lodging may increase when Tar Spot severity is high. Severe Tar Spot also reduces silage corn feed quality by reducing moisture, decreasing digestible components and reducing energy. No associated mycotoxins have been reported for this disease.

Tar Spot is spread by wind-driven rain and storms, plant residue, and machinery.

Yes, it overwinters in soil and residue and thrives in cool (60-70 degrees Fahrenheit) and humid conditions with prolonged periods of wet leaves.

Tar Spot can infest, form spores and reinfect in approximately 21 days.

  • Select hybrids with resistance to Tar Spot.
  • Consider applying fungicides.
  • Manage irrigation.
  • Rotate to other crops.
  • Manage residue.
  • Scout for Tar Spot.

To date, there is no evidence to indicate that Tar Spot in corn produces harmful mycotoxins.

If conditions are favorable for Tar Spot development early in the season, consider a twopass fungicide program using Trivapro® or Miravis® Neo fungicide at the V4-V8 corn growth stage and the VT/R1 growth stage.

If the risk of Tar Spot is lower, consider an application of Trivapro or Miravis Neo fungicide at the VT/R1 growth stage, which may also combat other yield-reducing corn foliar diseases.