Corn Tar Spot

By Ty Bodeis  |  July 15, 2022

Tar Spot

Corn is beginning to tassel in Michigan, and it is time to begin scouting your corn for Tar Spot. Most places in the state have had tar spot in them so the disease is there and ready to spread. All the disease needs is a period of leaf wetness to get started, this can be as simple as a heavy dew or fog. It is early in the infection window now so it is an ideal time to scout and catch the disease early so that yield protecting fungicides can be applied before the disease gets severe. Under optimal conditions Tar spot can devastate a field in a matter of a few weeks.

Tar Spot infection occurs under periods of prolonged leaf wetness. The prolonged period is more than 8 hours, which makes evening rains, dews and fogs the most problematic because they often keep the leaves wet for upwards of 12 hours. Once the infection is in the corn plants, after the leaf wetness period it can take two to three weeks for the easily identified black spots to begin appearing. If you have experienced any weather that can cause infection or expect to, a fungicide program may be warranted.

Effective fungicides have the ability to suppress Tar Spot in heavy infection situations. These situations are when there are multiple and regular leaf wetting events and mild temperatures. Dry weather and very hot temperatures in the 90’s will slow the progression of Tar Spot. If the weather in your area appears to support the development of disease or you find Tar Spot in your fields and want to spray them contact your local chemical supplier for effective fungicides. There is also some hybrid resistance or tolerance for Tar Spot. DF Seeds is a distributor of Legacy Seeds corn products, and we are working together to gather information on the most tolerant varieties to the disease. We are testing and gathering more information to be able to have Michigan performance ratings available now and in the future.

If you have any questions or would like us to walk your field with you reach out to me Ty Bodeis DF Seeds Research Agronomist at ty@dfseeds.com or your DF Seeds representative and we can walk your field with you and answer your questions.