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Disease Outlook

Disease pressure is showing up across the country’s corn acres and growers are looking for the best possible solutions to ensure a successful harvest. We spoke with AgriGold Agronomists Austin Merz and Joe Stephan about what they are seeing in their areas and how growers can fight back.

Common Diseases & Current Situation

In the west, Merz is starting to see foliar diseases spreading throughout the corn crop’s canopy.

“We have had timely rains in a good portion of Nebraska and irrigation has begun. This moisture is key for disease development since all fungal diseases require that moisture,” said Merz. “I saw my first lesions this season of Gray Leaf Spot in southeast Nebraska a few weeks ago.”

Merz says that Gray Leaf Spot is a key disease for growers to consider when making decisions about fungicide application. Stephan agrees that Gray Leaf Spot has historically been the largest yield robber but points out that modern hybrids are much more resistant to Gray Leaf Spot than those of several years ago.
“The recent hot and dry weather pattern in northern Indiana and most of the eastern corn belt has not been conducive to foliar disease thus far, but as the saying goes, ‘Just wait and things can change quickly,’” says Stephan. Merz noted that if Gray Leaf Spot lesions can be found on the ear leaf of the corn plant at or near tasseling, a fungicide application is likely warranted.

Both agronomists have concerns about Southern Rust in their area but have yet to see a significant presence at this point in the season. Merz says that the most high-risk fields are usually those that are planted very late and reaching reproductive stage later than normally expected.

“The aggressive nature and ability to spread quickly are what causes Southern Rust to become a major concern if it is found and favorable conditions persist,” added Stephan.
In the east, Stephan is looking out for Northern Corn Leaf Blight, Physoderma Brown Spot, and the newer disease Tar Spot. Both Physoderma Brown Spot and Northern Corn Leaf Blight seem to have been held at bay by the hot and dry conditions in Stephan’s area. Tar Spot has been found this year in Eastern Iowa, Southern Wisconsin, Northern Indiana, and Central Michigan and can be quite aggressive, spreading quickly under humid and wet conditions.

“Keep a close eye out for Tar Spot if you irrigate or begin to have heavy dews,” advised Stephan. “Fungicide applications will likely offer a return on investment if applied around VT when Tar Spot is infecting a field.”

Is Fungicide Application Appropriate?

Growers may be seeing less disease pressure than past growing seasons in many areas of the country, but that may not mean there is not a benefit to fungicide applications. Fungicides can help a corn plant mitigate stress outside of disease, such as drought and heat stress. Applying fungicide also helps improve late season standability going into harvest.
“Even with lower commodity prices, I feel growers should look at applying fungicide to protect every bushel of potential they have in order to stay profitable amid these trying times,” says Merz. “Across the industry, there have been trials showing good ROI with fungicides even with lower disease pressure.”
Both agronomists recommended dual mode of action fungicides that are preventative and curative, as well as having longer residual protection.

Looking Forward

Going into 2021, Stephan and Merz both advise looking at more seed characteristics than just plot yields.  “Talk with your seed rep or agronomist and pick out a portfolio of hybrids that can bring different features to your lineup, such as plant health,” said Merz. “Spread your risk by diversifying your lineup.”