Field Facts: Tar Spot | Inputs & Insights | Corteva Agriscience

Field Facts: Tar Spot

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Tar spot on corn leaf

Tar spot is a relatively new disease to the Corn Belt. It first appeared in the United States in 2015 and only started causing concern in the Midwest after a severe outbreak in 2018. Because tar spot is not as well known as other diseases, it has taken some farmers by surprise and caused significant yield loss. The infection has been shown to reduce corn yield by up to 50% in serious cases.

  • Common name: Tar spot
  • Scientific name: Phyllachora maydis
  • Symptoms: Symptoms first appear as circular, or ovular black lesions on corn leaves. These lesions typically start on the lower leaves and move up the corn plant. 
  • Conditions for development: Tar spot favors cool conditions (60 – 70 F), high relative humidity, frequent cloudy days and seven or more hours of dew at night. 

Fast facts

  • Tar spot was first identified in high valleys in Mexico in 1904 and has since spread to South America and parts of North America.
  • Under favorable conditions, tar spot can spread rapidly through the corn canopy, causing premature senescence of corn leaves. This is because the lesions the disease creates reduce the photosynthetic capacity of the leaves.
  • Severe tar spot infestation also can reduce stalk quality, which impacts the plant’s ability to defend against soil-borne pathogens, leading to issues like stalk rot and lodging. 
  • Serious outbreaks of tar spot have been shown to reduce corn yields by up to 50%.


Control tips

  • A strong fungicide can help control tar spot. Aproach® Prima fungicide offers two powerful modes of action against the disease.  Work with your local distributor or territory manager to determine proper timing of Aproach Prima for maximum control of tar spot. You can help your customers choose corn hybrids that are resistant to tar spot to avoid yield loss.
  • The Disease ID Guide from Corteva Agriscience provides detailed information. 

Aproach® Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.


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