Are you worried about Tar Spot?
July 16, 2024
You may have heard that this disease has been reported in Michigan.
You may have even started seeing this disease in your own fields. If you have not yet scouted for Tar Spot, look through the leaves for these spots of disease. These are not from the insects in your field. Tar Spot is embedded in the leaf, while insect frass is not and can be rubbed off.
Tar Spot can devastate Michigan corn fields. It starts with a fungus through the corn plant’s stoma. Long periods of specific conditions in the microclimate of your corn fields can reduce yields, lower test weight, and cause the corn plants to lodge. This makes harvest timing critical as the plants deteriorate quickly when Tar Spot infects your crop.
What are the chances your fields will get Tar Spot? Have your fields been wetter than average? This includes extended morning dews, lingering fog, and rainy days that extend the time the leaves are wet through the day.
Corn hybrids are not immune to Tar Spot, no matter what resistance rating is listed for that variety. Identifying genetics with strong resistance is ongoing. Whatever hybrid you planted, a fungicide application can help slow the disease development.
Research has shown all fungicides labeled for Tar Spot increased yield over untreated checks. The best timing is likely between VT (tassel fully emerged) and R3 (milk stage). In some cases, two applications may be warranted. This is dependent on the yield potential of your field as the current commodity price will influence the payback of the second application.
By using the Tarspotter app, you can include your field location, corn growth stage and fungicide applications to confirm the likelihood of getting Tar Spot. Most currently show the risk is “medium” for Michigan. The fungicide application is recommended when the risk is over 35%. However, if you have silage corn, irrigation, high-yielding fields, etc., you can adjust the threshold for your farm.
As always, contact your DF Seeds agronomist, DSM or dealer for more information and resources about combating Tar Spot in your corn crop this season.
