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Devise a plan to monitor and manage corn troubles

A cold, wet spring and delayed planting across the Midwest could mean increased loss to corn diseases later in the growing season. 

Delayed planting increases the risk of diseases occurring toward the end of the growing season, because it means later tasseling, according to Alison Robertson, an Iowa State University plant pathologist. Instead of occurring around the beginning of July, tasseling in the middle to end of July coincides with when diseases start to ramp up in the Midwest.

“If we’ve only just tasseled, then we’ve still got a lot more of our grain fill period to accomplish when those diseases are starting to increase,” she says.

Moisture Matters

Disease requires wet conditions to flourish. 

“Moisture, moisture, moisture. I cannot stress that enough,” Robertson says. “Temperature will give us different diseases but every single disease needs moisture.” 

Tar spot, northern corn leaf blight, and gray leaf spot could all be a concern to Midwestern farmers this year.

“They’re the diseases that we have to keep in mind every season because they overwinter in the region,” says Nathan Kleczewski, a plant pathology and entomology technical specialist for Growmark Inc. “Depending on the weather, one or more could flare up.” 

These diseases are caused by fungi, meaning any conditions that promote humidity could lead to greater outbreaks. 

“Typically, humidity is going to be enhanced after the canopy is closed,” Kleczewski says. “Mid to late in that vegetative stage, once those canopies close, they kind of act like a shelter for the humidity. It can hold that moisture a lot longer.” 

Get in the Fields

Scouting fields throughout the season is essential to understanding disease pressure. 

“Get out in your field every now and then and have a look to see what’s going on,” Robertson says. “Don’t wait until you’re sitting in the combine and come across a dead patch.” 

Kleczewski recommends scouting several spots throughout the field seven to 10 days before tassel, looking for signs and symptoms of disease. If diseases are present, fungicides can help limit yield loss. 

“Most of the research, even regarding tar spot, has shown the best time to apply a fungicide in most years is around tasseling through brown silk,” Robertson says. While earlier application is necessary in some situations, she says farmers should consider whether an application is a good use of resources. 

“You don’t want to be spraying a fungicide just because you have it sitting in your shed,” she says. “You want to make sure you’re going to get a return on that investment.” 

If disease pressure is evident, farmers should make decisions regarding fungicide as soon as possible. 

“Don’t wait until the last second to get a fungicide application out there,” Kleczewski says. “As we learned last year, when you have a lot of people making applications, there’s only so many sprayers to go around. You may call on Tuesday and not get an application made for 10 days. If you spray too late, it’s not going to be as efficacious and you’re not going to get your money’s worth.” 

Tools like the Tarspotter app and the Crop Protection Network can help farmers make management decisions. In fields where disease is a known issue, later-season standability tests can also be useful. 

“Just before physiological maturity, or R6, get into those fields and do some standability checks,” Robertson says. A push test — where you literally push on a stalk to see if it stands — can tip farmers off if they need to harvest earlier than planned. For fields with significant disease pressure, an earlier harvest may be necessary to maximize yield potential.

“If you do have a field with a lot of foliar disease pressure, those plants might yield less, but they also tend to dry up a little faster because of all the infection and loss of leaf area,” Kleczewski says. “Try to schedule those fields that are heavily infested for early harvest, because they will tend to have more lodging issues that can lead to yield losses and quality issues.”

Plan for Next Year

Keeping detailed records of the season’s disease pressure can help farmers make better management decisions next year.

“The easiest thing people can do before planting is to ensure that they have a rotation in place,” Kleczewski says. “These are diseases that are specific to corn. When you take corn out of the field, it allows that residue that the diseases overwinter and survive off of to decompose.” 

Consider seed choice and placement on fields with a history of disease.

“Some farmers are going to have a lot of racehorse hybrids that tend to be more susceptible to disease,” Robertson says. “You don’t want to put a racehorse-type hybrid in a low-lying field along the edge of a river where you get early morning fog. That will be a prime location for these foliar diseases.” 

Planting disease-resistant hybrids in risky fields or fields with a history of problems can limit disease pressure and yield loss. 

“Then it’s just a matter of other practices like rotation and tillage,” Kleczewski says. “Incorporate those practices into their programs to minimize the amount of local residue in the field.”

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