5 Questions to Weigh Your Corn Disease Risk this Season

Fungal diseases can take a heavy toll on your corn crop
Fungal diseases can take a heavy toll on your corn crop. A foliar fungicide application at tassel can help.

Will foliar diseases steal your corn yield this season?

“There’s always some disease risk every year,” said Thorsten Schwindt, Bayer fungicides product manager. The pathogens causing foliar diseases are always present in the environment.1 If you’re growing a susceptible corn hybrid, you could see blighted leaves, weakened stalks, downed plants — and disappointing yields.

Fungal diseases can take a heavy toll on your corn crop, easily stealing 10 percent of your yield, Schwindt adds. In severe infestations, yield losses can reach 30 percent or more, said Alison Robertson, Iowa State University plant pathologist.

Understand your risk of foliar diseases

It’s important to understand how the environment and your production practices affect your risk of foliar fungal diseases, said Carl Bradley, University of Kentucky plant pathologist.

If you answer yes to these questions, you may need to apply a foliar fungicide at tassel:

  Within fields, low spots that hold moisture are ideal places to start looking for disease

Within fields, low spots that hold moisture are ideal places to start looking for disease.

  1. Did you plant susceptible hybrids?
  2. Genetic resistance to common fungal diseases ranges from low to high, but there are no completely resistant corn hybrids, Robertson cautions. Late-planted corn is also more susceptible to fungal disease, she said, because plants are still pollinating and filling grain when disease risk peaks in late summer.

  3. Is the environment favorable for disease?
  4. Does the field have a history of disease? Is there a large amount of surface residue to harbor pathogens? More corn residue can lead to earlier and more severe infections, Bradley said.

  5. What is the field’s cropping history?
  6. Continuous corn and irrigated corn have a higher risk of disease, scientists say.2 Fields in river bottoms or low areas prone to mists or heavy dews are also more vulnerable, Robertson said.

  7. Is the weather conducive for infection?
  8. Gray leaf spot thrives in hot, humid weather. Northern corn leaf blight favors moderate temperatures and frequent rains. Southern corn rust likes warmer temperatures and can propagate very quickly with less moisture than other fungal pathogens.

    “It’s essential to understand foliar diseases and the conditions that favor each disease,” Robertson said. “If it’s hot and humid, for example, and you are growing a hybrid that’s susceptible to gray leaf spot, you’re going to want to spray a fungicide.”

  9. Do you see disease symptoms?
  10. “Know your fields,” said Randy Myers, Bayer fungicides product development manager. “Scout first where you’ve had disease issues in the past.” Within fields, low spots that hold moisture are ideal places to start looking for disease.

Stop corn disease at tassel time

When conditions are ripe for disease, a foliar fungicide application at tassel time (VT to R2) can ensure strong, healthy stalks; control infections; and protect your crop’s high yield potential.

It’s particularly important to protect the ear leaf and the two leaves above the ear, Myers said, because they are the plant’s “photosynthesis engine” – contributing the most to grain yield. “Plan to make an at-tassel fungicide application if you know there’s disease risk in your fields,” he adds.

And remember: If foliar disease injures your corn plants, the yield loss can’t be recovered. “Apply early, before leaf damage occurs,” Myers warns. “The triazole fungicides have curative activity, but they can’t fix damage that’s already been done. It’s important to be on the front end of infection so you can limit disease potential.”

Added benefit to fungicides: stalk strength

Treating foliar disease with a fungicide at tassel or soon after not only helps protect corn yield, but also helps maintain stalk quality, said Tamra Jackson-Ziems, University of Nebraska plant pathologist.

That’s because diseased corn leaves can’t produce enough sugars through photosynthesis to fill the ear, so the plant draws carbohydrates from the stalk to feed the ear, weakening stalk integrity. Weak stalks are more likely to snap off or lodge, hindering harvest.

“If growers are applying a fungicide to manage disease, they may get the added benefit of improved standability,” Jackson-Ziems said. “We’ve seen improved standability even in years when we didn’t see a lot of foliar disease or yield differences.”

In 2012 trials, Nebraska researchers found lodging scores fell significantly with a fungicide application at VT, compared to an untreated control – even though disease pressure was very low that year due to drought.3

Bayer solutions for late-season corn disease

To manage corn diseases, you need a well-planned program that includes proper hybrid selection, seed treatments and fungicide applications that provide multiple modes of effective action on diseases that are present.

Delaro® fungicide can help you achieve top corn yields. Its advanced formulation delivers unmatched, broad-spectrum disease control; best-in-class dual modes of residual action; and improved plant health. Count on Delaro to:

  • Prevent and cure. Delaro offers both preventive and curative defense against a broad spectrum of common fungal diseases, including gray leaf spot, northern corn leaf blightsouthern corn rust and anthracnose leaf blight.
  • Manage resistance. Delaro includes two long-lasting and effective modes of action — a strobilurin plus a triazole. Fungicides that kill pathogens in more than one way provide better disease control, Myers said. Using multiple modes of action in the same application is critical to managing pathogen resistance development. That’s essential for preserving the effectiveness of current fungicides.
  • Protect yields. In replicated, field-scale trials across the Midwest in 2016 and 2017, an at-tassel application of Delaro provided an average 3-bu.-per-acre yield advantage over Stratego YLD, Myers said. And fields with the Delaro application outyielded fields using Stratego YLD nearly three out of four times.
  • Boost plant health. Delaro helps plants use limited resources — such as moisture and nutrients — more efficiently, Schwindt said. It also helps ensure strong stalks, reducing lodging risk and improving harvestability.

Before applying any fungicide, please read the entire label for the best possible results and to confirm the product is effective on the disease you need to control. Not every product is suitable for every situation. Correct application technique will ensure the best results.

For more information on corn disease management solutions, contact Bayer.

© 2018 Bayer CropScience LP, 2 T.W. Alexander Drive, Research Triangle Park, NC 27709. Always read and follow label instructions. Bayer®, the Bayer Cross® and Delaro® are trademarks of Bayer. Delaro is not registered in all states. For additional product information, call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.cropscience.bayer.us.

Work Cited

1. Bradley, C. A. “Getting to Know the Foliar Diseases of Corn.” The 2015 University of Illinois Corn & Soybean Classic, University of Illinois, 2015, 22-25. http://extension.cropsciences.illinois.edu/fieldcrops/classics/pdfs/2015.pdf

2. Kleczewski, N. “Economics of Fungicides in 2014 Corn.” University of Delaware Cooperative Extension Field Crops Disease Management, University of Delaware, 2014, 7-20. http://extension.udel.edu/fieldcropdisease/2014/07/20/economics-of-fungicides-in-2014-corn/

3. Jackson-Zeims, T. “2012 Foliar Fungicide Product Comparison on Corn.” University of Nebraska South Central Agricultural Laboratory, 2012, 14. https://docs.google.com/viewer?url=https://cropwatch.unl.edu/documents/2012%20Foliar%20Fungicide%20Product%20Comparison.pdf

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