Frequently asked Questions about Crown Rot in Corn

Crown rot is a disease that has affected corn for decades but has recently re-emerged in importance as more farmers and professionals in the agriculture industry are observing crown rot. Crown rot is not well-understood, but research is ongoing to better understand many aspects of this disease. This publication will discuss what we know about crown rot and answer frequently asked questions.

What are the symptoms of crown rot?

Symptoms of crown rot are occasionally observed in the early-mid vegetative stages. Affected plants may be stunted, wilted, or have yellowed lower leaves. When the plants are dug up, brown to black discoloration of roots may be observed. If affected plants are split, the crown tissue may be discolored dark brown (Figures 1 and 2).

Crown rot symptoms are more commonly observed at the end of the season when corn is nearing maturity (dough through black layer). Affected plants often senesce early or die prematurely and may be referred to as “ghost” plants describing a grayish-green discoloration often observed (Figures 3 and 4). These affected plants are frequently surrounded by healthy plants.

Once corn has senesced, external symptoms are harder to observe. The interior pith of the crown will be discolored, and discoloration may extend to the first node or the roots. Roots and brace roots may have a pinkish or reddish color (Figure 5).

What causes crown rot?

The specific pathogen or pathogen groups that cause crown rot are still not well known. However, in recent years, diagnostic efforts in several states have observed that crown rot symptoms have been associated with various Fusarium spp. Fusarium is a wide and diverse genus that includes numerous species that are plant pathogens as well as beneficial fungi. Currently, it is unknown what species of Fusarium may be responsible for the symptoms we associate with crown rot, but research is underway to characterize the species associated with crown rot.

In addition to Fusarium spp., Rhizoctonia crown and brace root rot, caused by Rhizoctonia solani, has been observed sporadically throughout the United States. Additional pathogens, such as Pythium spp. infect corn plants early in the season. While Pythium is a well-documented seedling disease causing organism on corn, it is unknown if Pythium contributes to crown rot or if a complex of these or other pathogens is involved in causing crown rot.

Another fungus that has been recovered from plants with crown rot symptoms is Phaeocytostroma ambiguum. This fungus has also been reported as causing root, crown and stalk rot of corn in Australia, Brazil, South Africa, and Europe.

What conditions favor crown rot?

The fungi suspected to be associated with crown rot survive in the soil and crop residue. While the disease cycle of crown rot is unknown, it is commonly thought that infections occur early in the season, while disease symptoms manifest later in the season.

Conditions that stress plants can favor many diseases, including crown rot. It has been suggested that wet, compacted soils early in the season contribute to crown rot, but the disease has been observed in a variety of soil moistures and soil classes. It is still unknown what conditions predispose a plant to infection and subsequent disease development.

Does crown rot cause yield loss?

Plants that die prematurely may have reduced yield due to a reduced number of kernels per row, reduced kernel size and reduced kernel weight. Specific estimates of yield losses for crown rot are not currently available, as it is difficult to distinguish losses from stalk rots or other issues.

Speaking of stalk rots, are crown rot and stalk rot the same thing?

Fusarium stalk rot is also commonly observed in corn and although symptoms of stalk rot and crown rot can be observed in different areas of the stalk, it is plausible that the two diseases are related. The possible link between them is under investigation.

How do you determine if crown rot is the issue?

If crown rot is suspected, dig plants up and carefully remove the soil from the root ball, keeping the roots and the crown intact. Split the lower stalk and crown down through the root ball. If the crown and roots are discolored, consider sending the sample to a diagnostic laboratory for confirmation and to determine the causal organism. Many diagnostic laboratories may only provide a diagnosis of “Fusarium spp.” and not the exact species (for example Fusarium graminearum) associated with the sample.

What diseases can be confused with crown rot?

Red root rot (caused by Phoma terrestris and other species) can be confused with crown rot. This disease has been reported across many of the same areas and fields as crown rot. A deep red to purple discoloration of root and crown tissues are usually symptomatic of red root rot, compared to the dark brown to black discoloration often observed with crown rot. These similarities make it difficult to distinguish red root rot from crown rot in the field, and often samples must be sent to a diagnostic laboratory to determine the causal organism.

Is crown rot due to the accumulation of metals in the plant?

There is no evidence to indicate that crown rot is influenced or affected by metal accumulation in the plant.

What are effective management options for crown rot?

Hybrids vary in resistance, but it is difficult to determine crown rot resistance ratings. Ask seed dealers about crown rot resistance and note and avoid planting hybrids with crown rot problems.  

More research is needed to determine the effect of common practices such as crop rotation and residue management on crown rot. Crown rot is observed across a range of locations and production practices, indicating that these practices may not substantially reduce disease development.

Do seed treatments provide control of crown rot?

The impact of fungicide seed treatments on crown rot incidence or severity is not known at this time. More research is needed to determine what organisms cause crown rot and the range of infection timing to know if seed treatments will be effective.

Do in-furrow fungicides manage crown rot?

Multiple universities are testing in-furrow fungicides and additional products to gauge efficacy against crown rot, however, to date, no products have provided a consistent reduction of crown rot incidence or severity compared to non-treated controls. Research in this area is ongoing.  

What about early vegetative-stage foliar fungicide applications? 

Multiple universities are testing various foliar fungicide timings and products to determine efficacy against crown rot, however, to date, no product or fungicide application timing has consistently reduced crown rot incidence or severity compared to non-treated controls. Research in this area is ongoing.  

Why is crown rot such a difficult disease to work with?

We do not yet have a good understanding of this pathosystem. For example, it is not clear what pathogens are involved; when during the growth of the corn plants are infected; what conditions favor infection, and what conditions are necessary for crown rot to develop. Research is underway to understand these and other aspects of this important disease.

Acknowledgments

Authors

Alison Robertson, Iowa State University; Kiersten Wise, University of Kentucky; and Tamra A. Jackson-Ziems, University of Nebraska-Lincoln.

Reviewers

Tom W. Allen, Mississippi State University; Gary C. Bergstrom, Cornell University; Mandy Bish, University of Missouri; Martin Chilvers, Michigan State University; Alyssa Collins, Pennsylvania State University; Maira Rodrigues Duffeck, Oklahoma State University; Travis Faske, University of Arkansas; Andrew Friskop, North Dakota State University; Alyssa Koehler, University of Delaware; David Langston, Virginia Tech; Dean Malvick, University of Minnesota; Daren Mueller, Iowa State University; John Mueller, Clemson University; Pierce A. Paul, The Ohio State University; Edward J. Sikora, Auburn University; Damon Smith, University of Wisconsin-Madison; Darcy Telenko, Purdue University; Albert U. Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs; and Yuan Zeng, Virginia Tech.

Photo Credits

All photos were provided by and are the property of the authors and contributors

This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/private professionals that provides unbiased, research-based information to farmers and agricultural personnel. 

This article is published by the Crop Protection Network with funding provided by the National Corn Growers Association (NCGA), the United States Department of Agriculture – National Institute of Food and Agriculture (USDA-NIFA), and the Grain Farmers of Ontario through the Canadian Agricultural Partnership (CAP), a federal-provincial territorial initiative.