Crown rot is rearing its head across a wide swath of the Corn Belt this year, and growers need boots in the field now to identify which plants could lose their ability to stand prior to harvest.
Nicole Stecklein, a field agronomist based in east-central Iowa, says the disease problem is less about a particular hybrid this year than the relentless succession of stresses corn has endured since planting.
A Season of Relentless Stress
“Honestly, it’s not a huge shocker that we’re seeing a lot of crown rot this year because we have not been short on stress,” Stecklein says.
The list reads like a greatest-hits album of agronomic nightmares: wet conditions around emergence, crusting, heat and drought, saturated soils, wind, cloudy weather, nutrient losses and continued heat stress — all taking their toll on corn across much of the Midwest.
“Add on to that the amount of nitrogen that was lost when we tried to ‘drown it’ in June. Now it’s also got a nutrient stress as it’s trying to fill the grain,” Stecklein adds.
The result? Disease pressure that has lurked relatively inconspicuous until now, when stressed plants have little left in the tank to withstand infection.
Pathogens That Exploit Weakness
Crown rot is caused by a complex of fungal pathogens rather than one clearly defined organism. That makes it difficult to predict and manage with the same precision farmers can apply to some foliar diseases.
“Crown rot and stalk rot pathogens aren’t actually very good at their job,” Stecklein says. “What they are good at is exploiting stress of that plant.”
The pathogens can establish earlier in the season, but symptoms often become more obvious as the crop enters grain fill.
Stecklein says this unusual growing season also helps explain why crown rot is showing up in fields with different genetics and across a wide geography.
“What continues to be surprising is how absolutely widespread it is,” she says. “We used to be able to say, ‘Hey, this plant, these genetics typically have pretty healthy crowns. You don’t see a lot of crown rot.’ But we’re seeing it in very diverse genetics. It does not care who you are this year. Everybody is seeing a lot of this crown rot, and it’s because it’s mostly environmentally driven.”
Scout Now, Prioritize Harvest
For farmers, the immediate priority is determining which fields are most vulnerable to lodging, as a result. Those should move up on the harvest schedule.
“Crown rot this year is showing up in a big way across a big geography, and it doesn’t care who you are,” Stecklein says. “So it’s going to be important to go out, check your fields and know what you’re dealing with so you can make a priority list for harvest.”
She encourages farmers not to rely solely on what a field looks like from the road — dig up some plants and inspect the crown and lower stalk.
Look For The ‘Ghost’ Plants
That’s important because crown rot is a disease farmers may not recognize until late in the season. The Crop Protection Network (CPN) says symptoms are most commonly observed from the dough stage through black layer, when affected plants can senesce early or die prematurely. Those plants often take on a grayish-green color, earning them the nickname “ghost” plants.
That’s also the best time to determine whether a plant is dealing with crown rot rather than stalk rot, says Doug Gucker, University of Illinois commercial agriculture educator.
The distinction requires digging up some plants and splitting the stems down through the plants’ crown roots to inspect the internal tissue. Healthy corn stem tissue should be white, Gucker says. Tan or gray discoloration inside the crown is symptomatic of crown rot.
Although the symptoms of stalk rot and crown rot can be observed in different areas of the stalk, it is plausible that the two diseases are related, according to the CPN. The possible link between them is under investigation.
For a definitive diagnosis, Gucker recommends farmers submit a plant sample to their local lab for testing.
Recognize the Progression
Early symptoms of crown rot can include plants that may begin to turn purple as sugars accumulate in the leaves but aren’t being efficiently transported to the ear.
As the disease progresses, corn leaves become wilted, then brown and “crunchy.” The ear begins to tip downward. At that point, splitting the crown and lower stalk can reveal the rot.
“Maybe it’s just at a 45-degree angle, but when that ear starts to turn down, and when you open up that crown and that stalk, that’s when you actually start to see the rot. This stage is usually when people realize they have crown rot,” she says.
The problem can escalate quickly as stalk rot will readily move into already weakened, diseased plants.
In severely affected plants, standability becomes the overriding concern.
“This guy, you sneeze too close to him, and he’s going to fall over,” Stecklein says, pointing to one corn plant that’s essentially dead.
Management Starts at Planting
There is no rescue treatment that will reverse crown rot once the crown is infected.
Stecklein says management begins with reducing the opportunity for infection and helping plants remain as healthy as possible. That actually starts at planting, she notes.
“Number one would be watch your planting conditions, watch your emergence conditions,” she says. “Get this stuff out of the ground as soon as possible because the faster you get it up out of ground, the smaller the window Mother Nature has to infect this thing.”
She notes that fungicides aren’t a direct treatment for crown rot because infection occurs early and the crown is difficult for fungicides to reach.
“Fungicides in general do not do a great job of getting in there and actually stopping a crown rot infection because, A, it happens earlier and, B, they’re not going to get to the crown,” Stecklein says.
Watch Stecklein discuss various stages of the disease showing up in Iowa cornfields now, at the YouTube link below:
The Indirect Benefits of Fungicides
Fungicides can still have an indirect benefit, however, by protecting the plant from foliar disease and reducing the impact of additional stress.
“What fungicides did do this season and can do is decrease our level of stress — making the plant healthier, keeping away foliar diseases and decreasing stress — which is going to help this plant be able to fight that infection and stand longer,” she says.
The Action Farmers Can Still Take
For farmers heading into harvest, Stecklein’s message now is simply get in the field, split some stalks, assess standability and use what you find to prioritize harvest on a field-by-field basis.
“We’re really going to have to be on top of this corn crop this year because, in a lot of cases, we’re going to need to get to it before it falls down,” she says.
