CHATHAM, Ill. – With combines ready to roll in the northern Corn Belt, Great Lakes states and Dakotas, corn fields should continue to be monitored and scouted for stalk integrity or standability concerns before harvest. University and industry agronomists agree that checking fields prior to firing up combines can reduce harvest losses, reduce the stress of slow harvest and reduce future issues with volunteer corn.

Stalk rot is of particular concern to corn farmers in areas of excess rainfall as the 2026 harvest is underway, according to Matt Montgomery, agronomy education lead for Beck’s, blogger and farmer from Chatham. “The closing story for the 2026 corn crop is one of compromised stalk quality. Excessive rain and depleted nitrogen from the soil profile have hit many areas of Illinois, while excessive heat pummeled and bruised the crop as we entered September. The combination of these stresses has resulted in stalk cannibalization and increased susceptibility to stalk and crown rot,” Montgomery noted in his Sept. 16 “Short, Bald Agronomist” blog shared by the Illinois Corn Growers Association.

“Growers absolutely must keep an eye on fields for stalk and crown rot as harvest proceeds. Take the time to scout: push plants about 30 degrees off center (several inches at the top) to see if the lower stalk gives way. Examine brace root material, watching for roots that have wrinkled and gone soft. Pinch the lower stalk to check whether it collapses,” Montgomery added.

Field agronomists recommend that farmers not rely on a roadside visual analysis to determine whether crops are affected by stalk rot, as several stalk rot areas might be present in crop fields.

“(Corn growth stage) R5 is a great time to walk corn fields for yield estimates, check for early signs of crown and stalk rots that might make harvest a challenge, and evaluate the presence and severity of foliar disease symptoms. While itchy, it can be a very eye-opening experience,” said Meaghan Anderson, Iowa State University Extension and outreach field agronomist.

“Regardless of method chosen, check a minimum of 100 plants per field, preferably by evaluating at least 20 plants in five different areas. If more than 10 percent of plants in a field crush easily or lodge, this indicates stalk rot may be an issue, and that field should be prioritized for harvest,” according to Anderson.

“Each year may present special challenges in doing these checks. In years where downed corn is prevalent due to wind or root worm damage, farmers may need to use multiple field entrances to check different areas whenever possible.”

Corn is the only host of Diplodia stalk rot, a disease that overwinters as fungus within crop debris. Montgomery noted that infection can occur when the plant is stressed by dry conditions early, followed by ample rainfall around the reproductive period.

“Infection eventually reduces the pith (interior) of the stalk to a weakened, straw-like mass of vascular material. Eventually, the disease produces small black fruiting structures in the rind that cannot be ‘rubbed away.’ The presence of these small, immovable specks on the outside of the softened stalk helps identify Diplodia in the field,” he said.

Other culprits behind stalk rot include Anthracnose stalk rot, which can affect many different grass crops at various stages of development. Infection after pollination is typically of greatest concern, according to Montgomery.

Other types of stalk rots that can affect corn include Gibberella and Fusarium stalk rots, which often stain the interior of corn plants in a pinkish hue. Unlike with Diplodia, small black spots near nodes can be rubbed away.

“Regardless of the culprit, stalk and crown rot issues can point to a need for improved fertility management, stress mitigation and drainage. Hybrid selection favoring products better suited to handle wet feet or crown rot should also be considered to reduce future issues,” Montgomery blogged.

Stalk rot can lead to unharvested ears of fallen corn sprouting as volunteer corn the next season. Combines struggle to pick up fallen or tangled stalks properly, leaving whole ears or kernels loose on the ground, according to Bayer Crop Sciences. 

Iowa State Extension and Outreach posted the following tips for identifying and dealing with stalk rot of corn:

“Pinch test”

- Check stalk firmness by pinching the lower internodes near the ground between your thumb and forefinger.

- Be concerned when: stalks crush easily.

“Push test”

- Push the plant at shoulder height approximately 30 degrees from vertical.

- Be concerned when: plants pinch over, plants fail to snap back to vertical.