Tar spot of corn is a fungal disease that has been in Iowa and Wisconsin. Corn Pathologists always thought it would end up being spread to Minnesota. Late in September, it was confirmed for the first time in Minnesota. It was found in Fillmore County in South Eastern Minnesota. All the rain and high humidity likely favored the spread of the infection.

Tar spot is caused by a fungus named Phyllachora maydis. I am pleased they also call it tar spot, it's much simpler! The fungus causes small black spots on corn leaves and sometimes on the husk. They cannot be rubbed off and they do not break open like rust pustules.

Tar spot can cause significant yield losses that depending on weather, how severe the infection is and how soon in the growing season the infection occurs. If the fungus can survive in Iowa and Wisconsin I am sure it can in Minnesota too. I am going to ask my seed company dealers if corn hybrids are screened for or have resistance or some tolerance to tar spot just in case it becomes a real concern in Minnesota!

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