Keep Corn Rotting Diseases from Spoiling the Season
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Rotting diseases can turn a promising corn season nasty, often in just a very short time. Caused by a variety of different fungi, rotting diseases can lead to reduced yield, poor-quality grain, lodging and mycotoxin contamination, which poses a risk to human and animal health.1
Scott Heuchelin, Global Phytosanitary Risk Mitigation Lead, Corteva Agriscience, tracks trends in stalk, crown and ear rotting diseases. He shares some observations and advice you can pass along to customers.
FUSARIUM EAR ROT
Fusarium ear rot is dependent on environmental conditions, so it doesn’t necessarily appear every season. When it does, however, infection can lead to contamination with fumonisins, an important mycotoxin. “That’s a real concern, not just for production,” says Scott, “but when you have a greater area experiencing fusarium, a lot of grain elevators will start to dock growers on grain that tests positive for fumonisins.”
Fusarium ear rot is most likely to appear under very hot, dry, stressful conditions, often in the southern states and Great Plains. Growers in these parts of the country should look for hybrids with good fusarium scores, which are likely to perform as expected even under high pressures.
FUSARIUM CROWN ROT
Scott notes that this disease used to be more rare but has now increased in both frequency and distribution. As with many root and crown diseases, fusarium crown rot is most common in soils with poor drainage, such as hard pans or old lake beds. Scott says that more severe precipitation events have also contributed to the higher incidence of crown rot. “Instead of getting a quarter inch here, half inch there throughout the growing season, we’re getting dumped on with multiple inches of rain, which saturates the soils,” Scott explains. Saturation reduces room for oxygen around corn roots, killing off root hairs. This becomes a perfect entry point for disease-causing fungus. During the ear fill period, as nutrients are redirected to the ear of the plant, the fungus can then move up to the crown. “Once it colonizes the crown, it cuts off the nutrients for the rest of the plant,” he says. “That’s when you’ll see top dieback.”
ANTHRACNOSE STALK ROT
This disease has been declining some recently. “We’re not seeing as much severe stalk rot, dieback and premature death of plants anymore,” says Scott. It’s unclear if this is mostly due to environmental changes or incremental improvements from breeding. However, anthracnose stalk rot remains highly dependent on environmental conditions, so it can still be a problem when conditions are cloudy, warm and humid after silking.2
GIBBERELLA EAR ROT
The fungus that causes gibberella ear rot travels to ears if there are very wet conditions during silking. “The window for infection is actually very small — about a three- to four-day period right when the silks start to turn brown,” says Scott. Just as the silks are starting to senesce, they lose a little bit of their resistance. “The fungus can alight on silks that still have moisture in them and run down through the channel and into the ear,” he says. Mold then begins to form at the tip of the ear. “If you end up with really dry conditions, you can actually nip that in the bud in the tip of the ear and it won’t progress,” notes Scott. “But if you do get infection started and then you have wet, overcast conditions and frequent rains in the ear fill period, the disease will progress down the ear causing more and more yield loss and grain quality issues.” As the disease spreads, the level of mycotoxins present in the grain will also increase.
HEAD SMUT
This disease has decreased significantly over the past 10 years thanks to advances in breeding and seed treatments. Head smut fungus infects the roots of emerging plants. “If the apical meristem development can stay ahead of the head smut infection, you’ll end up with no infection and no spores being returned to the soil,” explains Scott. However, in dry soils or cold soils, emergence may be delayed, giving the fungus time to take hold. “The head smut can catch the apical meristem and become part of it,” Scott says. “As that plant grows, when the apical meristem differentiates into the meristems for the tassel and ear, they’re already infected.” Tassels and ears will then show symptoms of disease later in the season. Scott says farmer education has been another help in keeping the disease at bay. “In the areas that were having problems with head smut, we’re recommending they plant later in the spring.”
What can your customers do to stay ahead of corn rotting diseases?
Corteva is actively working to bring forward hybrids with better resistance to these diseases, but good management practices remain a critical defense. Because rotting diseases tend to be so condition-specific and appear in narrow windows of the season, timing spray treatments to disease appearance is often not practical. Instead, Corteva agronomists recommend managing for residues in the soil and in any bins or equipment. Since many rotting diseases enter plants through insect feeding damage, it’s also important to have an effective insecticide program in place, starting with seed treatments that offer protection from the season’s start. Finally, Scott offers a reminder that you can’t go wrong with measures that improve overall plant health, such as proper fertilization. “Any time you improve plant health, you end up with better resistance.”
A note about disease scoring: “Corteva has always taken a conservative approach in scoring our products for disease,” explains Scott. “We put our plants under extreme pressure, so that when the perfect environment comes along for that disease, we know that product will not perform any lower than the disease score we’ve released in the most recent years.” Since disease pressures can vary in different parts of the country, when a disease shows up, it might not always reflect its score. If the pressure is light, that corn is going to perform better than the score would indicate. But where the pressure is more intense, that corn is going to perform in alignment with its score. With this more conservative approach, your customers will have a better sense of what to expect when their corn is under disease pressure. Our goal is to ensure that the only surprises they experience during the season are pleasant ones.
1 Daisy Ahumada, “Corn Ear Rots: Managing Mold and Mycotoxins,” N.C. Cooperative Extension, July 15, 2024, https://content.ces.ncsu.edu/corn-ear-rots.
2 Anna Freije et al, “Diseases of Corn: Stalk rots,” Purdue Extension, February 2016, https://www.extension.purdue.edu/extmedia/BP/BP-89-W.pdf.
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