Identifying and Treating Tar Spot

The Dairyland Seed footprint has seen varying levels of tar spot infection ranging from none to areas that have seen infection for the past three or four weeks. The map below shows confirmed cases of tar spot. If you would like a more in-depth look, refer to our August 2 article found here:  https://www.dairylandseed.com/articles/tar-spot-update/

Confirmed Cases: Map as of 8/14/2023 Updated map can be found at https://corn.ipmpipe.org/tarspot/

Identification

• Small, black, circular, raised lesions (stromata) appear on leaves, husks, and tassels.
• Stromata cannot be removed from leaf tissue with water or rubbing.
  • Commonly misdiagnosed with frass (insect poop), rotten or aged pollen, and rust pustules. These can be removed by rubbing the leaf or scraping it with your fingernail.

Disease Triangle

Treatment

• Research shows the most advantageous timing of fungicide application to be VT to R2 (tassel to brown silk blister).
• Fungicides containing both a Group 3 (DMI Triazole) and Group 11 (Strobilurin) modes of action are the most effective with tar spot. You can find specific product efficacy can be found at the Crop Protection Network website.
• Fungicide treatments after the R2 to R3 timing have not shown to increase yields when applying for tar spot control. Therefore, R3 (milk stage) is the cut-off for applications of fungicide made for tar spot control in corn grown for grain.
• Fungicide applications in corn grown for silage should take into consideration the preharvest interval of the fungicide being applied. The preharvest interval (PHI) is the amount of time that must pass between application and harvest of the crop. Most fungicides have a 14-to-21-day PHI.

Brian Weller
Western Region
507.456.3034

Rod Moran
Western Region
507.456.3034

Dan Ritter
Central Region
219.863.0583

Branden Furseth
Northern Region
608.513.4265

Mark Gibson
Eastern Region
260.330.8968

Amanda Goffnett
Eastern Region
989.400.3793

Ryan Mueller
Eastern Region
989.400.3793

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