Corn Ear Rots | Weekly Crop Update

Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu

This has been a tough season on corn. The drought stress and heat of early summer impacted pollination and tip fill. Particularly in dryland fields, you may also be observing corn with lower test weights and more ear rots than usual. Ear rots can be caused by several different types of fungi. They can be problematic by reducing yield, kernel quality, and in some cases producing mycotoxins that are harmful to humans and livestock. Symptoms are often observed first at the tip of the ear but can be scattered throughout the ear. Infection usually occurs through silks and at locations of insect wounds. Hybrids with reduced husk coverage may have higher insect wounding and increased ear rot incidence. Both ear and stalk rots (see last week’s article) are favored by dry early season conditions that add stress to the corn plant. The table below highlights some of the most common corn ear rots.

Ear Rot	Fungus Name	Identification Features
Aspergillus ear rot	Aspergillus flavis	Powdery green to yellow-green spores. Often begin at the tip of the ear but can be scattered throughout. Associated with insect, bird, or hail injury and hot, dry conditions. Stressed plants are more susceptible.	Grey-green, powdery mold indicative of Aspergillus ear rot.
Diplodia ear rot	Stenocarpella maydis	White mold. Ears may drop early with bleached husk while corn plant is still green. Black raised bumps (pycnidia) may be visible on the husk, kernels, or cob cross section.	White mold on corn ear from Diplodia ear rot.
Fusarium ear rot (Pink Ear Rot)	Fusarium species	White, pink, gray colored kernels that can have streaking or “starbursts”. Can be clustered or scattered throughout the ear. May be present at stink bug or other insect wounds. This is the typically our most common ear disease.	Fusarium ear rot symptoms on kernels.
Gibberella ear rot (Red Ear Rot)	Fusarium graminearum (Gibberella zeae)	Pink or red colored molding. Typically begins at the tip of the ear. Silks and husk may stick to the ear from excessive mold. More common when it is cool and wet during the grain fill period.	Gibberella ear rot on hail damaged ear.
Penicillium ear rot	Penicillium species	Green to blue-green powdery mold, kernels may look streaked or bleached. Usually at the tip of the ear. Primarily occurs on ears with insect or mechanical damage. Fungus can colonize within the kernel causing a blue discoloration in the embryo known as “blue-eye”.	Penicillium ear rot at the tip of the ear.
Trichoderma ear rot	Trichoderma viride	Dark green mold on or between kernels. Often covers the entire ear. Associated with injury when ears are developing.	Trichoderma ear rot often covers the entire ear.

Of these ear rots, I have been getting the most questions about Aspergillus due to the mycotoxin it produces called aflatoxin. There are a few different types of Aspergillus, but Aspergillus flavus is the most common species. This is not a disease we often worry about. Colonization increases in years with drought-stress or if kernels have been damaged by insects or other causes. The powdery gray-green or yellow-green spores may puff like dust when you pull back a corn husk and grow on and between kernels. Aflatoxin is carcinogenic and regulated at an “action level” of 20 parts per billion (ppb). Corn contaminated at levels greater than 20 ppb cannot be sold for interstate commerce. Aspergillus has been present in VA this season and will likely be screened for at DE elevators as well.

A few things to keep in mind are:

There are many ear rots so not everything is going to be Aspergillus. If you have questions or need help with ID, let me know.
While Aspergillus mold increases risk of aflatoxins, just seeing mold does not guarantee that contamination will be high. Contamination can also vary from kernel to kernel.
If you do have a field with Aspergillus, while we cannot reduce the preharvest contamination at this point, steps can be taken to reduce postharvest aflatoxin contamination.

If you think you have a field with aflatoxin, harvest as soon as corn reaches maturity. Infection is favored by broken or damaged kernels, so take time to adjust combine settings and try slower header speeds to minimize kernel damage. Increasing fan speed can help to remove cracked or light-weight underdeveloped kernels to reduce contaminated grain. In cases where you are storing your grain, it is recommended to harvest at higher moisture to reduce field exposure, but corn should be dried to 15% moisture or less as quickly as possible (within 24-48 hours). It is important to match drying capacity to holding capacity of wet corn. Problems are more likely in dryland fields than irrigated, so it is best to harvest outside of the pivot separately and store that grain separately so that good corn is not contaminated. Follow good sanitation and clean out previous season debris from bins.