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Release Date: 11/15/2022

By:  Dr. Jerry Wilhm, North Central Research Station

Tar spot of corn has become a top concern of Michigan corn growers. Since the first confirmation in Allegan County in 2016, tar spot has since been detected in each county of the lower two-thirds of the Lower Peninsula. Recent research has identified several strategies to give at least some level of management against this disease. First, various fungicide products have proven effective while also showing yield-enhancing results. Second, application timing can affect control results where applications at later stages such as R2 were more effective than at pre-tassel or later R stages (R5). Third, hybrids have been identified that show higher levels of tolerance to infection (though not completely resistant).

Given these control strategies, there is still one major research gap and that is fungicide application placement. There is a relatively new method of application where the fungicide is sprayed down in the canopy mainly directed at the ear leaf and nearby leaves. This is the 360 Undercover from 360 Yield Center (Figure 1). The 360 Undercover has a nozzle cluster on supports from the boom that runs between the corn rows and has three nozzles. Two nozzles are aimed at the ear leaves on either side and a third nozzle is directed to leaves above the ear. This provides a “wall” of coverage to the sides plus upward movement. This system, in combination with the overhead boom, has been shown to greatly increase coverage of the corn foliage.

To date, the following treatments have been applied to two corn hybrids, one tolerant to tar spot and one susceptible to tar spot: boom application on 5-foot corn, boom application at R3, boom + 360 Undercover application at 5-foot corn, and boom + 360 Undercover application at R3. The fungicide product chosen for the trial was Veltyma (BASF; 7 oz/acre). Drone imagery of the plots, chlorophyll readings of corn leaves, and yield data will be collected from each treatment.

Despite low tar spot disease pressure across the state this year, including at the trial field, Dr. Jerry Wilhm had this say about the value of this research to Michigan corn farmers, “The farmer in me is glad we have avoided tar spot in 2022, but the researcher in me wished that there was some level of infection as I feel that the treatments we designed and applied would have been valuable for the future, as I don’t believe that we have seen the last of tar spot. However, the experiment will continue so as to determine the effects of these treatments on other and “hidden” diseases.”  

To share details of this research project, as well as other important tar spot information, the Corn Marketing Program and the North Central Research Station hosted a Tar Spot Tip Off event at the 2022 Agro Expo. The event had a meal and a field visit for growers followed by ice cream and discussion and collaboration. There were approximately 70 growers in attendance (Figure 2). The CMPM-supported research plot was showcased, and the treatment strategies generated good discussion. Additional tar spot presentations from BASF and MSU personnel also generated questions and discussion and made the event successful and informative.

Upon completion of this research project, data will be analyzed for trends and the results will be published in the CMPM annual research report, which will be released in early 2023.

Figure 1: NCRS research agronomist Tim Duckert describes the 360 Undercover designed to increase fungicide penetration down into the corn canopy.

Figure 2: Tar Spot Tip Off field day showcasing NCRS tar spot research plots.