Corn Ear Molds in 2023

Ear molds are starting to show up in some areas. If gone unnoticed, ear molds will continue to develop in the field through the fall, even after the corn reaches physiological maturity and begins to dry down. These fungal diseases are living organisms, and like any living organism, heat and moisture increases their activity. Proper identification of these molds is important because some are capable of producing mycotoxins. If the disease becomes significant enough in the field, it can cause docks at the elevator in the harvested grain and can spread within a grain bin if not dried properly. There are no rescue treatments for these diseases; however, timely harvest can prevent further spread of the disease in the field.

Diplodia Ear Rot

Diplodia ear rot, Stenocarpella maydis, is easily identified by its white-to-grayish-brown mold growing on and between the kernels of the ear. The mold usually starts at the base or in the middle of the ear and progresses to the tip. Diplodia ear rot can also be identified from the outer husk of the ear. You can often see black specks scattered on the husks. The specks are pycnidia, the spore-producing structures of the fungus. Pycnidia overwinters on corn debris and becomes the source of the infection the next year. 

Often times, the ears are infected with this particular ear mold as soon as 21 days after silking, a stage where the ear is very susceptible to infection. Since the pathogen overwinters on corn debris, no-till corn-on-corn situations are at a higher risk for infection. Dry conditions prior to silking and wet conditions after silking are also very favorable for disease development. Tillage or rotation away from corn will help reduce Diplodia in the soil. Diplodia impacted grain can have lower test weight and in severe cases can cause storability issues.

Giberella Ear Rot

Giberella ear rot, Giberella zeae, is most easily identified by its pink or reddish color and “fuzzy” fungal bodies on and between kernels. The infection begins at the tip and moves towards the base. Infection generally occurs during cooler periods, 2-3 weeks after silking. Giberella overwinters in corn residue as well as wheat residue that was infected with Fusarium head blight, which is the same pathogen. Large scale infections of Giberella can cause grain quality issues by producing mycotoxins such as Deoxynivalenol or DON and vomitoxin. These mycotoxins can cause issues when fed to animals, especially swine. Testing of suspect grain is preformed to determine levels of DON.

Fusarium Ear Rot

Fusarium ear rot, Fusarium verticillioides, looks different from the other two rots mentioned previously. Fusarium infects the corn ear in patches or on single kernels and tends to show up more often when there is damage to the kernels caused by hail, insects or birds. The kernels turn tan or brown and the mold appears to be white, gray or pink in color. The symptoms on the kernels typically begin as white streaks called “star bursts,” where the mold grows under the seed coat. Infection is more severe during warm and dry conditions.

Fusarium ear rot is caused by three species of fungi. Two of the species can cause fumonisins, a group of mycotoxins that affect humans and livestock. Since the three fungi exhibit similar symptoms, a lab test is needed to properly identify the infecting fungus. If there is potential for fumonisins, then you should follow recommendations for harvesting and handling contaminated grain. 

Aspergillus Ear Rot

Aspergillus ear rot, Aspergillus flavus, is identified by powdery olive-green fungal structures often accompanied with white or black structures as well. Hot and dry growing conditions with otherwise stressed plants favor infection. Aspergillus creates a mycotoxin in the kernel called aflatoxin. Aflatoxin is harmful and can cause a number of health issues for animals if large amounts of grain are infected. Stress mitigation through proper fertility, as well as drought tolerant hybrid selection. can help reduce chances of infection.

Ear Mold Management

If you find a field with ear molds, plan to harvest that field as soon as you can. Don’t delay harvest. Due to the overwintering nature of these fungal pathogens in corn, cultural practices such as crop rotation and tillage, along with selecting hybrids with lower susceptibility against ear molds, will aid in slowing the development of these diseases if present in the field. Since ear molds are highly variable in frequency and severity from year to year, screening for ear mold tolerance is a challenge for all seed companies.  Certain base genetics do vary in their susceptibility to the different ear rots, but other hybrid characteristics and weather play a big factor as well.

The information in this article is not meant to incite fear, but rather be a guide to help recognize ear molds and potential problems if they appear in your field. If you have any questions, please contact your Dairyland DSM or Regional Agronomist.

Brian Weller
Western Region
507.456.3034

Rod Moran
Western Region
507.456.3034

Dan Ritter
Central Region
219.863.0583

Branden Furseth
Northern Region
608.513.4265

Mark Gibson
Eastern Region
260.330.8968

Amanda Goffnett
Eastern Region
989.400.3793

Ryan Mueller
Eastern Region
989.400.3793

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