Corn Disease Treatment: Ensuring Healthy Crops

Corn plant diseases pose a serious threat on Nebraska farms each growing season. These pathogens can spread quickly under the right conditions. Left untreated, they can compromise a corn plant’s ability to grow and produce grain — affecting everything from food supplies to ethanol production.

“There’s a lot of different diseases and they can be caused by fungi and bacteria, nematodes and viruses,” said University of Nebraska professor of plant pathology Tamra Jackson-Ziems.

Corn disease treatment requires careful monitoring, advanced technology and hard work.

Many plant diseases need specific conditions to thrive. For that reason, it’s common for corn farmers to face similar diseases every year, even if they solve the problem the year before.

“Most of the time [the diseases we see are] pretty consistent. That’s usually because the pathogens that cause them, like some of the fungi, they’re very well adapted to our environment and so they’re able to overwinter,” said Jackson-Ziems, who also serves as a University of Nebraska Extension specialist. “So, once a farmer has to deal with a disease, most likely they’re going to see it again year after year if conditions are favorable again.”

Here are some common corn diseases in Nebraska:

Southern rust is a fungus. Along with common corn rust, which is similar, it causes rust-colored, blister-like bumps on corn leaves. Infections reduce the plant’s ability to photosynthesize, potentially leading to lower yields and poor grain fill. Like many types of fungus, it is most likely to infect corn during warm, wet and humid conditions.

“They grow inside the plant and then we can see symptoms of that, such as spots on the surface or eventually as they mature, rust fungi will burst through the surface and so that particular disease is actually ripping thousands of tiny holes in the leaves,” Jackson-Ziems said. “For the health of the plant, that makes it hard for the plant to regulate water. And so that’s very detrimental to the plant if there’s a lot of it.”

Southern rust cannot survive Nebraska winters, but its spores can travel to the state each spring.

“When Southern rust develops south of us, the south winds blow the spores up [to Nebraska],” she said. “So, all of us are watching pretty diligently to see when those [spores] arrive or…if they arrive south of us in states like Oklahoma and Kansas. It gives us a little bit of a heads-up when we might expect them later.”

Gray leaf spot is a fungal disease in corn that appears as narrow, rectangular gray or tan lesions on the leaves. The spots start at the bottom of the plant and spread upward. It reduces the plant’s ability to photosynthesize, which can lead to lower yields and poor grain development. The fungus survives in corn residue and spreads through wind and rain.

Although gray leaf spot was a problem for many years, Jackson-Ziems said it’s been less of a problem recently thanks to availability of resistant corn hybrids.

A disease that’s been more problematic recently is tar spot. Another fungus, it’s identified by small, raised black spots on the plant’s leaves. The spots get bigger and more plentiful the longer the plant is infected. It prefers warm, humid conditions.

“We first found it in the United States over in Indiana and Illinois and it spread east and west and north and south from there,” Jackson-Ziems said. “It’s becoming increasingly common here in Nebraska.”

Currently, she said tar spot has worked its way about halfway across the state of Nebraska.

Goss’s wilt is a bacterial disease in corn that creates gray, light yellow or tan lesions and dark green to black water-soaked spots. It can lead to yield loss by killing leaf tissue, reducing photosynthesis, and in severe cases, kill the corn plants.

Similar to how humans can get a bacterial infection through a cut in skin — the wilt enters plants through cuts in the leaves caused by hail, wind or insect damage.

“That actually opens up a wound for these bacteria to get in,” Jackson-Ziems said. “And, so even good disease-resistant hybrids still get Goss’s wilt and it can cause quite a bit of loss for our farmers.”

The bacteria that cause Goss’s wilt can survive Nebraska winters in corn residue left in the fields after harvest, so it can infect the same field multiple years in a row.

Farmers treat corn plant diseases through a combination of prevention, monitoring and active management. They often rotate crops — alternating between planting corn one year and another crop, such as soybeans, the next year — to break disease cycles. Another method is to use corn hybrids that were developed to be resistant to particular diseases.

“When farmers are aware which diseases they’ve had in the past, they can try to select corn hybrids from the seed company that might perform better against it or might have more natural resistance,” Jackson-Ziems said.

When necessary, farmers treat their fields with a corn pesticide. They also are constantly scouting their fields. Watching fields for signs of disease and tracking the corn growth stages are both vitally important aspects of the care of corn plants after planting.

Farmers use a variety of tools and technologies to treat or prevent corn diseases, including:

• Industry monitoring services — Tools such as forecasting maps and the Crop Protection Network, a service that maps reports of various corn diseases, let farmers know which diseases to watch for in their area.
• Resistant Hybrids — Specially developed corn varieties that resist specific diseases like Goss’s wilt or gray leaf spot can reduce crop losses to those diseases.
• Fungicides and Sprayers — Precision sprayers apply fungicides efficiently when disease risk is high— enabling farmers to only treat areas sick or at risk, increasing sustainability by using less product overall.
• Crop Scouting Tools — Drones, satellite imagery and mobile apps help detect disease symptoms in their fields early on, allowing them to treat plants before the disease advances.

Although farmers can’t control if weather conditions are ripe for a particular corn disease outbreak, they can reduce damage by taking preventive measures, scouting their fields for signs of disease and treating issues as soon as possible.

Timely treatment gives corn the best chance at recovering before the plant is mature, potentially allowing farmers to save their crop. In doing so, they keep the world supplied with the raw materials for corn-based food products, biofuels like ethanol and other products containing corn that we use every day.