ANKENY, Iowa (DTN) -- Crown rot is showing up in Iowa corn fields, and possibly other parts of the Corn Belt, according to Iowa State University Extension field agronomists. Experts urge farmers to scout fields now to prioritize infected acres for harvest.

Rebecca Vittetoe, an ISU Extension agronomist covering east-central Iowa, said crown rot has become more prevalent in the latter half of August. The pathogen or pathogen groups that cause the disease remain poorly understood, according to the Crop Protection Network (CPN), but its effects are clear: reduced water and nutrient uptake, resulting in stunted growth, premature death and poor stalk quality that can lead to lodging. Together, those impacts can reduce yields.

"I encourage farmers to get out and scout fields now. The general rule is if at least 10% of the plants in a field have crown rot, or stalk rot in general, that's a field you will want to harvest as soon as the corn is mature," Vittetoe said.

CROWN ROT SYMPTOMS

Crown rot is occasionally observed in the early to mid-vegetative stages, according to CPN. Affected plants may be stunted, wilted or have yellowed lower leaves. When the plants are dug up, roots are typically brown to black. If affected plants are split, the crown tissue may be discolored dark brown.

The disease is most detected late in the growing season as corn approaches maturity. Infected plants often die prematurely and take on a grayish-green appearance, earning them the nickname "ghost plants." Those plants frequently stand out because they are surrounded by otherwise healthy corn.

Meaghan Anderson, an ISU Extension field agronomist covering central Iowa, said she's excited about the yield potential of this year's corn crop. Southern rust isn't as widespread in Iowa and surrounding states like last year, which severely reduced yields in many areas.

However, Anderson said crown rot is rearing its ugly head. "I am worried about the sustainability of this crop (because of the fungal disease), as I'm seeing a surprising amount of it. There are quite a few ghost plants out there.

"It seems to be highly variable in fields based on hybrid," she continued, noting disease pressure isn't widespread. "It's important to evaluate fields now because as the crop continues to mature and plants dry, crown rot will be harder to spot."

When farmers can easily push over infected plants, or plants break off, farmers will want to harvest infected field as soon as possible, she said.

WHAT NOW?

There are few foliar or seed/soil-applied chemistries that provide consistent protection and control of crown rot, according to Bayer Crop Science and CPN. Researchers continue to study the fungal disease to better understand its causes and identify effective management strategies.

In addition to prioritizing fields with more than 10% crown rot incidence for early harvest, agronomists encourage farmers to track which hybrids are most affected.

"There's really nothing farmers can do treatment-wise, but hybrids vary in their level of resistance," Vittetoe said. "By documenting which hybrids are impacted, farmers can have informed conversations with their seed dealers about future seed selection."

Learn more about crown rot here: https://cropprotectionnetwork.org/… and here: https://www.cropscience.bayer.us/….

Matthew Wilde can be reached at matt.wilde@dtn.com

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