During the fall of 2018, considerable rainfall was received across some northern Corn Belt areas. This created an ideal environment for ear rots such as Diplodia, Gibberella and Fusarium that thrive under high-moisture conditions. The pathogens for these diseases can be viable for several years in the soil.
Diplodia ear rot can occur during rainy periods from the time of pollination to about three weeks after. Diplodia only infects corn and survives on residue; therefore, infection is most likely in continuous corn and in fields in which there is a considerable amount of corn residue from a previous crop. Prior to harvest, look for husks that have died prematurely (Figure 1). These are typically most apparent at the R5 and R6 growth stages. Also, look for ears that may still be erect while the others have dropped to their normal mature state. When the erect ears are husked back, you may find the white Diplodia fungus, generally starting at the base of the ear. Even if the fungus is only at the base of the ear at R5 growth stage, it can continue to colonize ears – especially if wet weather persists through harvest. Diplodia ear rot is not harmful to humans or livestock.
Gibberella ear rot is a white to pinkish to reddish mold that starts at the tip of the ear and progresses toward the base of the ear (Figure 2). It is more common in seasons with cool, wet weather from silking to harvest. The fungus has the potential to produce the mycotoxins vomitoxin and zearalenone. Vomitoxin can be very harmful to swine.
Fusarium ear rot-infected kernels are white to pink, appear cottony and are scattered around the ear (Figure 3). The infected kernels also have white streaks that are arranged in a starburst pattern. The mold can produce fumonisins, which is a mycotoxin. Fusarium ear rot is slightly different than Diplodia and Gibberella ear rots because it typically occurs during a period of drought during silking followed by high relative humidity (not necessarily rainfall).
For 2019, crop rotation and heavy tillage can help reduce the amount of pathogen-harboring corn residue. Additionally, maintaining a good fertility regimen, selecting corn products with insect protection, and selecting corn products with less susceptibility to ear and stalk rots can help reduce the risk of moldy grain. Planting different products with varying maturities is also a good way to help reduce the risk from a host of problems and should be a solid management practice for your farm. In-season ear rot management is limited since few fungicides and antifungal products are available for specific ear rots.
Identify and manage corn ear molds. Agronomy ALERT. Channel.com. http://www.channel.com/agronomics/Documents/AgronomicContentPDF/IdentifyandManageCornEarMoldsAlert.pdf
Management of Diplodia stalk rot and ear rots in corn. Agronomy ADVICE. Channel.com. https://www.channel.com/agronomics/Documents/AgronomicContentPDF/ManagementofDiplodiaStalkandEarRotsinCorn.pdf