Crown Rot – A Complex Issue in Corn Production

What is Crown Rot?

Crown rot is a complex disease. Infection takes place in seedlings early in the season, but symptoms are not readily apparent until the crop is in the grain fill stages and nearing maturity. Many questions remain about crown rot. Currently, the pathogen(s) that cause it, when infection occurs, any link to stalk rots, and viable management options are still not fully understood.¹ While crown rot has been observed in corn for years, the frequency and severity has recently increased. This disease is known to increase the risk of stalk lodging and has an associated reduction in yield potential.

Pathogens That Can Cause Crown Rot in Corn

Various Fusarium spp. have been observed in association with crown rot in corn, and efforts are underway to identify the specific Fusarium species associated with the disease.² Several other fungal pathogens have also been associated with crown rot, either individually or in combination with a complex of pathogens. Rhizoctonia crown rot and brace root rot are both caused by Rhizoctonia solani but tend to occur only sporadically across the Corn Belt. Pythium spp. are known to cause infection early in the growing season resulting in seedling diseases, but current evidence is unclear as to the extent to which Pythium may contribute to crown rot when interacting with other pathogens.¹ Colletotrichum graminicola, the fungus that causes anthracnose, has also been found in dead crowns infected with crown rot.³

Environmental and Field Conditions That Favor Disease Development

While specific environmental conditions that favor the development of crown rot have not been identified, a common assumption is that infections occur early in the season under cold, wet conditions followed by hot, dry conditions later in the season, which cause stress. The pathogens currently thought to be associated with crown rot are all soilborne and can overwinter on corn residue, and the development of these pathogens is encouraged by cold, wet, and compacted or poorly drained soil and cold air temperatures that can stress young plants.

During the 2024 growing season, fields in areas of the eastern Corn Belt—including parts of Illinois, Indiana, and Kentucky—experienced cool and wet conditions early in the growing season. These conditions were followed by timely rains in July, along with the effects of Hurricane Beryl. Very little rain was then received through August and September. Stalk cannibalization and early plant death were observed going into harvest along with faster than normal drydown of the grain. These weather conditions coincided with a greater incidence and severity of crown rot than had previously been experienced in those areas.

Symptoms of Crown Rot

If observed during early to mid-vegetative (V2 to V7) growth stages, stunted or wilted plants with yellowing lower leaves may be showing early symptoms of crown rot, however plants may exhibit no above ground symptoms until grain fill. In plants experiencing crown rot, an examination in the V-stages will typically reveal a dark brown discoloration, rather than the usual white-green indicative of a healthy plant, as well as brown or black roots (Figure 1).

Symptoms of a Fusarium infection are most apparent in later growth stages, usually from R4 (dough) to R6 (black layer), although in some cases they may be visible earlier. Affected corn plants die prematurely, turning a grayish-green color often referred to as “ghost” plants. These ghost plants can occur randomly as individual stalks or as groups of stalks surrounded by healthy plants (Figure 2). A discoloration of the crown can be seen by digging up the roots and splitting the stalk all the way through the crown. The discoloration can also extend into the lower internodes (Figure 3). Darker brown may indicate a more severe infection. Nodal roots and brace roots of infected plants may have a reddish color.^1,4 Since the crown tissue becomes rotted, the flow of water and nutrients in the vascular tissue (xylem) becomes disrupted which can lead to cannibalization of the stalk during grain fill, increasing the risk of stalk lodging.

How to Determine if a Crown Rot Infection Has Occurred

If observed symptoms on a corn plant indicate that a crown rot infection may have occurred, plants should be dug up including the root ball. Remove as much soil as possible while taking care to leave the roots and root crown intact. Carefully cut through the stalk and crown to check for discoloration. If discoloration is found, samples should be submitted to a diagnostic laboratory so that the pathogen(s) can be identified.

Can Other Diseases Be Confused with Crown Rot?

Red root rot, caused by Phoma terrestris and other species, can be confused with crown rot since it produces a red discoloration of the root and crown tissues (Figure 4) which can also be seen with infections from Fusarium or Gibberella. Dark discoloration can possibly be attributed to anthracnose. A laboratory analysis is needed to confirm which pathogen is present in the infected tissue.

Impact on Grain Yield

Because crown rot can disrupt the flow of water and nutrients inside the corn plant, late season stresses can lead to premature death, likely resulting in a reduction of kernels per row, kernel size, and kernel weight. Harvest losses may also increase due to a potentially higher incidence of stalk lodging. It can be difficult to separate the amount of yield loss due to crown rot alone, since stalk rots or other disease may have combined effects on final yield potential. The Crop Protection Network estimated that crown rot (pathogen not specified) was responsible for yield losses of over 22 million (M) bushels of corn in the United States in 2022. This placed crown rot fourth behind tar spot (116M), fusarium stalk rot (55M), and nematodes (48M) in terms of bushels lost in the northern states of the Corn Belt in 2022.⁵

Management Options for Crown Rot

Seed-Applied or In-Furrow Fungicide Treatments

Multiple studies by universities have been inconclusive, as the seed-applied and in-furrow fungicide products available today have not been consistent in reducing crown rot incidence or severity. It is generally assumed that seed applied fungicides are not active long enough to provide adequate protection from crown rot pathogens past the seedling stage.¹

Foliar Fungicide Applied in Early Vegetative (V) Growth Stages

Similar to the research findings with seed-applied or in-furrow products, a foliar fungicide application in the V5 to V6 growth stages has not been consistently effective at managing crown rot.¹ The translocation of most foliar fungicide products occurs only within the leaves to which they were applied, so the protection would not extend to newer leaves. If any translocation of a fungicide through the plant were to occur, it would most likely move via the xylem, and thus upward through the plant, limiting the potential for any product to reach the crown.⁶

Manage Factors That May Induce Stress to the Corn Crop

• Seeding at recommended rates for a given corn product can help alleviate stress which may be introduced by plant densities beyond the ideal range of the corn product.
• Improve areas of poorly drained soils.
• Reduce insect and/or nematode feeding on the roots.
• Avoid planting into cool, wet soils.
• Provide adequate irrigation, if available, especially during growth stages with high water demands.
• A fungicide application at the VT to R1 growth stages may improve overall plant health and reduce stress to the plant which could come as a result of a foliar disease infection, especially in the upper canopy.

Crop Rotation

Rotate to a crop that is not a host plant for any of the pathogens that may cause crown rot.

Select Corn Products That Have Tolerance to Crown Rot and Other Diseases

Genetic resistance to crown rot can vary widely among corn seed products. Check with your local seed supplier to see if ratings specifically for crown rot are available for their corn product lineup. In addition, high tolerance to foliar or stalk diseases can help reduce overall stress to the corn plant, increasing the plant’s chances of being able to fight off infections.

Sources:

¹Robertson, A., Wise, K., and Jackson-Ziems, T.A. 2023. Frequently asked questions about crown rot in corn. Crop Protection Network. https://cropprotectionnetwork.org/publications/frequently-asked-questions-about-crown-rot-in-corn

²Byamukama, E. and Mathew, F. 2022. Fusarium root and crown rot developing in corn. South Dakota State University Extension. https://extension.sdstate.edu/fusarium-root-and-crown-rot-developing-corn

³Munkvold, G. 2002. Crown rot symptoms common in corn. Iowa State University, Integrated Crop Management News. https://dr.lib.iastate.edu/handle/20.500.12876/17995

⁴Robertson, A. 2021. End of season thoughts: stalk rot, ear rot and tar spot. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/blog/alison-robertson/end-season-thoughts-stalk-rot-ear-rot-and-tar-spot

⁵Mueller, D., Wise, K., and Sisson, A. 2023. Corn disease loss estimates from the United States and Ontario, Canada – 2022. Crop Protection Network. https://cropprotectionnetwork.org/publications/corn-disease-loss-estimates-from-the-united-states-and-ontario-canada-2022

⁶Robertson, A. 2023. Is a fungicide application to corn at V5 a worthwhile input? Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/blog/alison-robertson/fungicide-application-corn-v5-worthwhile-input

Web sources verified 11/14/24. 1211_466301