Tar Spot is a fungus called Phyllachora maydis. It’s really becoming an issue across Northern Illinois, Northern Indiana and Wisconsin. Universities in each of these states are trying to evaluate and come up with some best management practices on how to combat this disease. Fellow agronomists and I have also been scouting plots and trying to come up with some answers also.  We are all in the “Research phase” of this new disease and I will sum up what we know to date.

After looking at a fair number of fields infected with Tar Spot last year, my fellow agronomists and I feel that this fungus is more of a secondary disease stress issue. We feel if a corn field is infected with a severe leaf disease, poor fertility, continuous corn anything that puts a “stress” on the plant, Tar Spot sets in as a secondary organism that ends up intensifying leaf and stalk necrosis, plus could hinder kernel fill if the plant is infected early. If you plant a corn hybrid that has average health, continuous corn or fertility that is not the best. I would definitely lean toward using a fungicide especially if you are in a “high risk” zone.  I added a map to the bottom of this article that Bayer puts out biweekly showing the counties with a higher probability of infection.

Tar spot is a new disease with a lot of “unknowns” on best management practices.  There will be a learning curve the next few years but there are some management practices that will help combat this new disease.  Keeping that plant happy and healthy as long into the season as we can will help fend off severe infection.  Crop rotation, healthy hybrids, fungicides and a good fertility program with late season nitrogen application should all help to prevent severe infections of tar spot.  LG44C27, LG5465, LG5565, LG59C72, LG59C46, LG60C33, LG62C02 and LG62C35 are some of the better LG Seeds products that we noted in last year’s plot tours that had high ratings against Tar Spot.

References and additional information:

https://badgercropdoc.com/2018/08/29/holy-tar-spot-batman/ damonsmith

http://cropdisease.cropsciences.illinois.edu/?p=822

https://www.extension.purdue.edu/extmedia/BP/BP-90-W.pdf