Midwest Corn: Stalk Rot and Nitrogen Loss, Try the Pinch Test – DTN

    Left: Fusariumm Ear Rot; Right: Gibberella Ear Rot. Photo: South Dakota State University Extension

     Jay Magnussen can’t think of one reason why his stalks would be at risk for lodging this year.  

    Instead, he can think of three — right off the top of his head.

    First, there was the wet spring in northwest Iowa that forced his corn to form shallow roots. Then came the nitrogen loss, as that rainy weather slogged into the month of June. To top it all off, he has now spotted anthracnose stalk rot creeping up the stalks in some of his fields — another gift from the soggy season that has delivered 9 to 10 inches above the region’s normal rainfall.

    “It actually looks to be a pretty good crop, all things considered, so I’m advising everyone to get out there and check stalks and harvest early,” said Magnussen, who farms and works as an agronomist at his local co-op near Paullina, Iowa.

    Stalk rot, root problems, nitrogen loss — anything else?

    “There was a period in May where we went through growth stages really rapidly,” added Matt Montgomery, a Pioneer agronomist in west-central Illinois. “The corn gets a little brittle-boned, and it does predispose you to stalk issues.”

    Ample moisture in much of the Midwest also gave foliar diseases plenty of opportunities this season. Gray leaf spot was particularly prevalent in the Corn Belt this year, Montgomery said. Other usual suspects like northern corn leaf blight, Goss’s wilt and bacterial leaf streak of corn have also surfaced throughout the growing season. More recently, a newer disease called tar spot has been darkening fields in Illinois, Michigan and Wisconsin late in the season this year.  All these diseases can threaten stalk quality, because they destroy leaf tissue and jeopardize photosynthesis.

    Finally, the widespread drought conditions that plagued the southern and western edges of the Corn Belt — Kansas, Missouri and Oklahoma, in particular — will definitely weaken plants, as they cannibalize their stalks to fill ears during grainfill, Montgomery added.

    Enough to convince you to go scout your fields?

    Montgomery recommends you stop at a dozen places within a field, at least 50 paces apart, and give your plants a hearty shove.

    “Push them 30 degrees off center, and if 10% or more crimp off, mark which fields are like that and get in those fields first for harvest,” he said.

    If you left your protractor at home, Magnussen can help. “Just grab above the ears and bend each plant over until the top of the stalk hits the next row,” he said. He recommends checking fields when the corn has reached black layer and moisture levels are near 28% to 30%.  

    Magnussen also does the “pinch test” at the bottom of his stalks for good measure and carries a pocket knife for some quick disease scouting.

    “I take a knife and cut the plant off at the ground, split the stalk and try to identify if different stalk rots caused this,” he said. “I like to know which one it is, so I can select a hybrid that has better resistance to that pathogen next year.”

    Nitrogen loss in corn can be identified by the lower leaves of the plant yellowing prematurely, Magnussen added. The yellowing will take on a V pattern, with the tip of the V pointed toward the stalk, he said.

    For help identifying and managing any stalk rots you might find in your field, such as Anthracnose, Diplodia or Fusarium, check out this Purdue University guide:….

    DTN crop disease models monitor for gray leaf spot and northern corn leaf blight in corn. Customers can retroactively look back on maps to see if and when they were at most risk for these diseases at

    Emily Unglesbee can be reached at

    Follow her on Twitter @Emily_Unglesbee

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