When corn ear rot takes hold, it can have a devastating impact on your yields. And ear rots aren’t just harmful to your bottom line; they can also pose serious risks to animal and human health. When mycotoxins in corn contaminate grain due to ear rot, it becomes difficult to market and often brings lower prices.
Between 2012 and 2023, corn ear rot infections caused $8.6 billion in grain damage.1
Several corn ear rot species can infect your fields, each one with different symptoms, damage, and toxins produced. Identifying the type of corn ear rot in your fields will enable you to reduce yield losses, protect grain quality, and avoid costly surprises at harvest. Recognizing early signs of infection is key to staying ahead of the problem.
This article provides a guide to the different types of corn ear rot you’re likely to find in your fields. Comparing and contrasting symptoms will help you identify ear rot, allowing you to make informed management decisions for your crop.
Aspergillus ear rot in corn
Symptoms
When you pull back the husk from an ear of corn and find dusty, olive-green mold on the tip of the ear, you have Aspergillus ear rot.2 If the disease has had time to develop, it may infect the entire ear.
Timing
The spores can survive on above-ground corn residue and will infect ears at R1 and into late silking.
Risk factors
Aspergillus ear rot is most likely to occur in hilly, dry parts of the field. The fungus thrives in hot, dry conditions and is more prevalent in the Southern regions of the United States. Stressed plants with nutrient deficiencies or those impacted by hail, drought, or insect damage will be the most susceptible.
Mycotoxins in corn
One of the significant risks associated with Aspergillus ear rot is the mycotoxin it produces, known as aflatoxin. Aflatoxins are known to be carcinogenic and cause liver diseases in livestock. Younger animals are most susceptible to aflatoxins and can die from contaminated feed.3
Aflatoxins are extremely hardy, surviving through heat treatments and boiling.4 While there are alternative uses for grain with Aspergillus ear rot, contaminated grain will negatively impact marketability.5
Diplodia corn ear rot
Symptoms
Diplodia ear rot manifests as a white mold at the base of the ear and lives between the kernels. Eventually, the mold will colonize the entire ear, turn a brownish color, and cause the kernels and ear to become soft. It can also lead to lightweight, “mummified” ears.6
If you suspect you have Diplodia ear rot, snap an ear in half and look at the kernels. You often will see black specks, called pycnidia, at the base of each kernel.
Timing
The fungus can survive in above-ground crop residue, and corn is susceptible to Diplodia ear rot up to three weeks after silking.
Risk factors
If your corn is silking (R1) and the weather has been dry, but then your crop gets wet from rain or irrigation, you may want to start scouting for Diplodia ear rot. The spores will live on corn residue and are spread by rain splashing on the dry soil. Fields that are no-till or continuously planted with corn will be more vulnerable to Diplodia ear rot infections.
If you have had a high incidence of Diplodia ear rot in your fields in the past, you’ll want to identify those areas and harvest them earlier to prevent spread and damage.
Mycotoxins in corn
Fortunately for US farmers, mycotoxins haven’t been found in Diplodia populations in the US. However, many livestock will refuse to eat moldy grain, so it can still hurt your on-farm livestock feed efficiency as well as grain prices when you go to market your corn.7
Fusarium ear rot in corn
Symptoms
Fusarium ear rot can be challenging to identify. The fungus may infect seedlings and grow inside corn stalks without showing any visible symptoms. When symptoms do appear, they can vary from ear to ear.
Some infected kernels may look tan or brown, while others develop a pink or salmon-colored mold. You might also spot white streaks across the kernels, known as “starburst” patterns. This is caused by the fungus growing underneath the pericarp. Unlike other ear rots that cover the entire ear, Fusarium typically affects scattered kernels or small patches.
Timing
Fusarium can infect plants early, even at the seedling stage, and continue to develop in kernels as they mature. The fungus often grows without clear external symptoms, which makes early detection difficult.8
Risk factors
Ears damaged by insects such as corn earworm, European corn borer, or even birds are more vulnerable. Wounds in the kernel surface provide easy entry points for infection.
Unfortunately, Fusarium ear rot can occur in a wide variety of conditions. However, it is typically found in warm parts of the field, where high humidity and stress from drought or nutrient deficiency can make ears more vulnerable. Because the fungal spores thrive on corn residue, continuous corn fields with abundant residue can experience repeated infections over time.
Mycotoxins in corn
Fusarium ear rot may not always impact yield, but it can contaminate grain with fumonisin, a harmful mycotoxin. Fumonisins are dangerous to both humans and animals, especially swine and horses.9 What makes it more concerning is that harmful levels of fumonisin can accumulate even when fungal symptoms are barely visible. These levels are more likely to spike when hot, dry conditions are followed by humid weather.
Testing for Fusarium ear rot is essential because contaminated grain may be rejected or docked by grain buyers due to feed safety regulations.10
Gibberella ear rot in corn
Symptoms
Gibberella ear rot infects the corn silk channels, appearing as a pink to white mold at the tip of the ear. It tends to be one of the easier ear rots to identify in the field.
The mold grows between the kernels and underneath the husk. If conditions are right, the mold may cover large portions of the ear, and the husk and silks may stick closely to the ear. This can give the ear a “mummified” look.11
Timing
Gibberella infects ears during silking, especially when the weather is cool and wet. Once established, the fungus can continue to develop on the ear even after physiological maturity.
The spores will overwinter on corn residue on the soil surface and can infect small grains and soybean roots.
Risk factors
Since Gibberella can infect corn, small grains, and soybeans, fields with continuous corn or planted after infected wheat can be highly susceptible. Cool weather with excessive rain in the fall, particularly at and after silking (R1), can lead to an increase in infections.
Mycotoxins in corn
Gibberella ear rot is a major producer of deoxynivalenol (DON), more commonly known as vomitoxin, and zearalenone (ZEN). Vomitoxin is one of the most common types of mycotoxins in food.12 They have been known to cause nausea, vomiting, diarrhea, headaches, and fevers in humans.13 High concentrations of vomitoxin can also be problematic when fed to swine.14 Grain with high DON levels is often rejected or priced lower by grain buyers, and thresholds for DON in feed and food are strictly regulated.15
Grain with high levels of ZEN can impact reproduction hormones in swine. However, there are no FDA guidelines in place for ZEN contamination levels in corn.16
Identifying corn ear rot early is essential to protecting both your yield and grain quality. By recognizing the unique symptoms and risk factors associated with each type, you can take timely action to minimize losses and prevent mycotoxin issues. Regular scouting, residue management, and informed harvest decisions are your most effective tools for controlling corn ear rots.
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.
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Endnotes
- Wise, Kiersten, et al. “An Overview of Ear Rots.” Crop Protection Network, 12 Nov. 2024, https://cropprotectionnetwork.org/publications/an-overview-of-ear-rots.
- Wise. “An Overview of Ear Rots.”
- Wise. “An Overview of Ear Rots.”
- Wrather, Allen, et al. “Aflatoxins in Corn.” University of Missouri Extension, May 2010, revised Sept. 2017, https://extension.missouri.edu/publications/g4155.
- Wise. “An Overview of Ear Rots.”
- Wise, Kiersten, et al. “Diplodia Ear Rot of Corn.” University of Kentucky College of Agriculture, Food & Environment Extension Plant Pathology, Plant Pathology Fact Sheet PPFS-AG-C-05, https://plantpathology.ca.uky.edu/files/ppfs-ag-c-05.pdf.
- Paul, Pierce and Anne Dorrance. “Diplodia Ear Rot.” C.O.R.N. Newsletter, vol. 2016, no. 30, Ohio State University Extension, 2016, https://agcrops.osu.edu/newsletter/corn-newsletter/2016-30/diplodia-ear-rot.
- Woloshuk, Charles, and Kiersten Wise. “Fusarium Ear Rot.” Purdue Extension, BP-86-W, Sept. 2014, https://extension.purdue.edu/extmedia/bp/bp-86-w.pdf.
- U.S. Food and Drug Administration. “Guidance for Industry: Fumonisin Levels in Human Foods and Animal Feeds” Center for Food Safety and Applied Nutrition and Center for Veterinary Medicine, Nov. 2001, https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-industry-fumonisin-levels-human-foods-and-animal-feeds.
- Wise. “An Overview of Ear Rots.”
- Wise. “An Overview of Ear Rots.”
- Willyerd, Katelyn T., Pierce A. Paul, and Peter Thomison. “Gibberella Ear Rot and Mycotoxins in Corn: Sampling, Testing, and Storage.” Agriculture and Natural Resources, Ohio State University Extension, Apr 7, 2016, https://ohioline.osu.edu/factsheet/plpath-cer-04.
- Sobrova, Pavlina, et al. “Deoxynivalenol and Its Toxicity.” Interdisciplinary Toxicology, vol. 3, no. 3, 2010, pp. 94–99. U.S. National Library of Medicine, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984136/.
- Wise. “An Overview of Ear Rots.”
- Wise. “An Overview of Ear Rots.”
- “From Aflatoxin to Zearalenone: Key Mycotoxins You Should Know – Zearalenone.” Penn State Extension, 12 Dec. 2023, extension.psu.edu/from-aflatoxin-to-zearalenone-key-mycotoxins-you-should-know-zearalenone.
