The Titan Blog

Tar Spot Corn Disease

Titan Pro
July 19, 2019

As wet, moderate weather persists, farmers should be on the lookout for tar spot, a relatively new disease identified in 2015. Theories indicate the pathogen arrived in the U.S. from storms that originated in Mexico and Latin America. Last year, heavily infected fields incurred yield losses of 30-40 bu. per acre. Tar spot symptomology is like common and southern rust; however, tar spot has small black lesions, may have halos, and cannot be rubbed off.

Tar Spot Disease Cycle Information

  • P. maydis and M. maydis only infects corn
  • Develops only when P. maydis coexists with M. maydis
  • Becomes pathogenic and highly contagious when both fungi are present
  • M. maydis is commonly found on the surface of corn leaves
  • Might be transported on fresh or dry corn leaves or husks
  • Disease development generally starts at flowering time
  • Infection in the leaves can occur as early as the V8 to V10 leaf stage
  • Lesions appear on the lower leaves and moves rapidly up the plant
  • Favors cool temperatures (60-70 *F) and high relative humidity
  • Infected corn plants leaves can be completely covered in tar spot 3 to 4 weeks after flowering

Should you find tar spot in your fields, contact your Titan Pro Regional Account Manager, provide photos, and field location.


(Photo courtesy of Martin Chilvers, Michigan State University)

As wet, moderate weather persists, farmers should be on the lookout for tar spot