The Midwest corn crop has endured a pressure cooker of disease problems this season.
Now, the aftermath of stress from disease and weather extremes in many areas are contributing to anthracnose top kill, according to Ken Ferrie, Farm Journal Field Agronomist.
“A lot of people think their corn is going through natural drydown at this point, but that’s not the case,” he says.
How To Tell The Difference
Ferrie explains the visual differences between the photo finish you want to see in corn and what happens when top kill sets into the crop:
The Desired Drydown Process: The husk should be ripening while the two leaves below the ear are green. In addition, above the ear the plant will be green all the way to the top of the plant. It should be dying slowly from the bottom up.
Anthracnose Top Kill: With this problem, you will see a green husk and the top two leaves will be dead or dying.
“Some farmers may confuse top kill with one of the rusts this year because the top of the plant could be yellow to orange in color. But rust comes from the ear zone and goes north to the top of the plant, while top kill shows up at the top of the plant and goes down,” Ferries explains.
Another clue to whether anthracnose was the cause of top kill (as opposed to high temperatures), Ferrie tells growers to look for black spores on the outside of the lower stalk of dead plants.
“When you split the top of the stalk, you’ll see discoloration. The more the hybrid is stressed, the quicker the problem shows up,” he says.
While fields that were sprayed with a fungicide later in the season tend to show the least amount of anthracnose top kill, fungicide does not stop it.
“We don’t have a fungicide for anthracnose top kill, but the healthier your plants are the less of the problem you’ll likely find,” Ferrie says.
Yield Loss Potential At This Point
“If your crop is at late R5 moving into R6, and the top of that plant is solid, it should finish strong,” Ferrie says.
But when top kill comes in 15 to 20 days before black layer, Ferrie says it hurts late-season kernel fill. This is particularly true in newer hybrids, which often build a lot of their yield late in the season.
Those hybrids will be pushed to black layer faster and at the cost of kernel depth.
Ferrie advises farmers to start conducting stalk push tests at 30- to 40-degree angles in their crop to see if the stalks will buckle, and to plan their harvest accordingly.
“With this stress from top kill, things will speed up and harvest will be here sooner than later for some growers and, unfortunately, with less yield,” he says.
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