Tar Spot of Corn Map
Tar spot is caused by the fungus Phyllachora maydis. Tar spot is still a relatively new disease in the United States and Canada and tracking its past and current distribution can help us learn more about the disease. Counties, provinces or parishes that are highlighted in yellow on the map have had tar spot confirmed by University extension personnel and/or diagnostic laboratories in this current growing season.
If tar spot has been confirmed in a county/parish, this should encourage you to scout your fields for this disease. A confirmation of tar spot does not mean the disease is severe or a fungicide application is needed. For more information about management of tar spot, please read An Overview of Tar Spot, and see the table below which provides possible benefits from applying fungicides based on when tar spot is first detected in an area and conditions that favor further development.
Crop Stage When Tar Spot is First Detected | Possible Benefit From Spraying | Comment |
|---|---|---|
Late Vegetative | Rarely, consult extension specialists before spraying | Scout fields and monitor disease progress; may need a second spray |
VT/R1 (Tasseling/Silking) | Yes | May need a second spray |
R2 (blister) | Yes | Less likely to need a second spray |
R3 (milk) | Yes | No second spray needed |
R4 (dough) | Maybe, with severe disease pressure | No second spray needed |
R5 (dent) | No | No second spray needed |
R6 (black layer) | No |
The current map displays data for 2025.