Corn ear rots pose a significant challenge for farmers across the country. From 2012–2024, ear rot fungi cost farmers $8.6 billion in yield loss, according to the Crop Protection Network (CPN). Reduced grain quality due to the presence of mycotoxins can cut even further into the farm’s bottom line.
With no rescue treatments, management for ear rots must start early and last season-long to prevent profit loss.
“While infections can be variable [year to year], losses overall are going up,” said Tyler Harp, a technical product lead for Syngenta. “If you haven’t done any management before you have an infection and mycotoxin accumulation, there’s not a lot you can do.”
Common Ear Rots and Mycotoxins
In the U.S., there are several problematic ear rot diseases that are caused by different fungi.
“Even if you don’t see visual symptoms of ear rot, most of these fungal species produce toxins,” said Pierce Paul, a cereal pathology professor at Ohio State University. “Toxins are secondary chemical compounds that help the fungi cause damage to the ear,” he said. “Once those toxins cause problems in terms of human and animal health, they’re considered mycotoxins.”
A General Guide to Corn Ear Rots
Aspergillus
Mycotoxin Produced: Aflotoxin
Favored Conditions: Hot and dry
Signs and Symptoms: Olive-green spores
Fusarium
Mycotoxin Produced: Fumonisins
Favored Conditions: Moderate to warm temperatures during silking, wet periods before harvest
Signs and Symptoms: White to pink-purple mold scattered across ear; starburst pattern in kernels
Gibberella
Mycotoxins Produced: Deoxynivalenol (DON or vomitoxin) and zearalenone
Favored Conditions: Cool and wet
Signs and Symptoms: Pink to white mycelial growth
Penicillium
Mycotoxin Produced: Ochratoxin (some species)
Favored Conditions: Wet and humid after grain fill
Signs and Symptoms: Blue-gray fungal spores
Trichoderma
Mycotoxin Produced: Trichothecenes (some species)
Favored Conditions: Damaged corn
Signs and Symptoms: Blue-green spores growing in and on kernels; may cause sprouting
Diplodia
Mycotoxin Produced: None currently known in the U.S. and Canada
Favored Conditions: Moderate temperatures, wet during silking
Signs and Symptoms: White mycelial growth on ear and husk; black pycnidia in cob
Nigrospora
Mycotoxin Produced: None
Favored Conditions: Damaged corn
Signs and Symptoms: Black spores, gray mycelia, shredding cob
Cladosporium
Mycotoxin Produced: None
Favored Conditions: Wet weather near harvest
Signs and Symptoms: Dark-green to black kernels
Risk Management
While ear rot diseases are seen nationwide, the level of infection and mycotoxin contamination can vary greatly.
“Knowing what drives the disease is also informative in terms of what you can do to minimize those risks,” Paul said.
Manage Residue
Fungal pathogens can survive in corn residue, so corn-on-corn acres and low-till operations are at a higher risk for ear rot infections. Wheat can also be a host crop for problematic fungi, such as Fusarium graminearum, and should be considered when planning rotations.
If ear rot infections become a recurring issue, rotating to a non-host crop or implementing a form of tillage is a strong first step to reduce risk.
Seed Selection
Hybrid selection is also important to consider. Although no hybrids fully resist ear rots, some options are less susceptible than others.
“A combination of some form of residue management to reduce the survival of that fungus in combination with a moderately resistant or less susceptible hybrid would be a good strategy,” Paul said.
Fungicide Options
Although a relatively new management option, some foliar fungicides are labeled for certain ear rots. Fungicide applications for ear rot control are most effective when made around the silking (R1) growth stage.
“Fungicides are more valuable when they are used preventatively because you’re protecting the plant through a critical stage,” Syngenta’s Harp said. “If a disease comes in before the application, a good fungicide may stop the infection, but it can’t rewind the damage that is already done.”
Consider other disease risks and fungicide longevity when timing applications. For example, tar spot is often seen later — with significant yield damage — in the season. If tar spot is a concern, consider utilizing a longer-lasting fungicide or making an application from R1 to R3.
Meredith Operations Corp.
Weather Conditions and Scouting
The right weather conditions can greatly exacerbate infections.
“If the crop is silking, or in other words, pollinating, and you have a number of consecutive days with wet, humid conditions, that’s a sign you could have ear rot and mycotoxin contamination problems,” Paul said.
Scouting for ear rots should happen in the weeks leading up to harvest. Peel back ear leafs in several sections of the field to look for kernel discoloration and mold growth.
Each ear rot disease appears differently, so the ability to identify each is crucial to understanding potential mycotoxin infection levels. Because mycotoxins are harmful to humans and livestock, the Food and Drug Administration established action and advisory levels for the compounds. As a result, high levels of mycotoxins can lead to a discounted price, or rejection, at the grain bin.
Testing Mycotoxin Levels
The CPN recommends testing grain if at least 10% of the field is moldy, or if the grain is being used to feed livestock. Visual tests alone cannot accurately identify all potential problems, so further testing is recommended.
A representative sample should weigh at least 4.4 pounds, according to the USDA Grain Inspection Handbook. Several subsamples should be taken and combined into a single composite sample.
Tests can be done using a testing kit or by sending samples to a professional laboratory. The CPN recommends working with your local Extension office to determine the best option in your area.
Saving Grain Quality
While no rescue options are available, measures can be taken to reduce the impact on grain quality and profits.
“If you suspect you’re at risk, based on weather patterns or the hybrid you’ve planted, you can scout to make decisions about harvest,” Paul said. “If a field is at risk, you probably want to harvest that field early, even if you harvest at a slightly higher moisture content and then dry it down.”
Using a grain cleaning method during harvest can also reduce mycotoxin levels. Fine, broken pieces carrying a high level of contamination are often seen following an ear rot infection. Adjust the combine to blow out those lightweight kernels and other broken pieces, Paul recommended.
A quick drying and cooling process can limit fungal growth prior to storing infected grain. The CPN recommends drying infected grain to less than 13% moisture and cooling it to 30°F.