To manage corn ear rots, it is important to first properly identify them. Corn ear rots can be a significant pest, and they are dependent upon environmental conditions and the presence of an inoculant to become an issue.
"Essentially, different fungi will colonize in the ear kernels and make the corn ears rot," said Heather Kelly, Extension researcher in plant pathology and IPM coordinator for the University of Tennessee, during the virtual Milan No-Till Field Day. "This can lead to not only poor grain quality and lower yield and test weights, but some of these fungal pathogens can also create mycotoxins."
Mycotoxins are toxic compounds produced by fungal pathogens when the right environmental conditions occur.
"These toxic compounds can be carcinogenic and can cause different issues for humans and animals when consumed," she said. "It's important when storing grain to make sure any corn ear rot is identified to know what needs to be done for harvesting. Even if you harvest, store, and dry your grain correctly, you're not going to reduce the amount of ear rot or mycotoxin already present in the grain, but you can eliminate any additional ear rot or mycotoxin by drying it down to the right moisture."
A few significant corn ear rots occur in Tennessee, including Aspergillus, Fusarium, Gibberella, and Diplodia. A general management tip for reducing or preventing corn ear rot is to reduce plant stress.
"Reduce plant stress through proper fertility management, proper planting density, irrigating when needed, as well as managing for insect damage," Kelly said. "Additionally, some hybrids have a tolerance to ear rots. If you've had a field with a certain ear rot and are continuing to plant corn in the field, you want to try to pick a tolerant or less susceptible corn hybrid."
Aspergillus corn ear rot
Aspergillus has yellow to olive-green patches of spores on or between the kernels, and while any of the kernels can be infected, Aspergillus usually begins at the tip of the corn ear. It is also a hot, dry-loving ear rot.
"Aspergillus is most severe under drought and hot, dry conditions, during pollination and grain fill. This is a concern in Tennessee due to years of extremely hot and dry conditions," Kelly said. "Depending on your hybrid and field situation, you might start to see some Aspergillus ear rot forming, which can reduce the overall weight of infected kernels. Aspergillus can also result in aflatoxin, which is the most carcinogenic mycotoxin in corn ear rots."
This reduces grain quality, and the aflatoxin can increase even after harvest if the grain is not dried below 15% moisture and stored in at least 50 degrees Fahrenheit.
"The mycotoxin that comes with Aspergillus has an action level threshold, 20 parts per billion for human consumption," she said. "This means docking or rejection of grain loads with this level of aflatoxin."
Management strategies for Aspergillus include irrigating to reduce plant stress as well as reducing any additional stressors from nutrient deficiencies, planting densities, or insect damage. A product on the market, Afla Guard, can also be used effectively by applying it before tassel.
Fusarium kernel ear rot
Fusarium features both similarities to and differences from Aspergillus.
"Fusarium also likes hot, dry conditions to develop," Kelly said. "Unlike Aspergillus, Fusarium has a white, cottony growth in between and on kernels, and it dries down the kernels, turning them tan to brown with white streaks in a starburst pattern."
The yield penalty includes reduced grain quality as well as producing a mycotoxin.
"Fumonisins are the mycotoxins these pathogens can create, and they're acutely toxic to animals," Kelly said. "It can cause blind stagger disorders in pigs and horses, and it's also been linked to increased cancer rates and other human health problems."
Wheat and some rotational crops can host these pathogens, so it is important to identify this issue early to manage for it.
"Going forward, try to find hybrids that have resistance when you plant corn in fields where Fusarium has been a problem," Kelly said.
Gibberella corn ear rot
Gibberella, caused by a Fusarium species, has a reddish mold appear usually at the tip of the ear, and then it grows downward. In severe infections, the growth will colonize the ear so tightly it will be hard to pull the husk back from the corn ear. Favorable circumstances are wet and cool conditions after the silking stage.
"When Gibberella starts infecting and colonizing, it can continue to develop in the ear after R6 and/or until grain moisture is below 18%," Kelly said. "Under extended periods of rainfall that delay drying, it can continue to increase and become more severe."
Insect damage can enhance disease infection and increase severity.
"It is also one ear rot which can produce two different mycotoxins, zearalenone and vomintoxin, also called DON" she said. "Both mycotoxins are harmful, but for those contaminated with DON, animals may refuse to feed on the grain or even have breeding issues if consumed."
Early harvest and immediate dry-down to 15% moisture is the best management option with Gibberella corn ear rot and for future seasons rotation out of corn and wheat to reduce inoculum buildup and tolerant hybrids when planting back to corn.
Diplodia corn ear rot
Symptoms for Diplodia include bleached husks while the rest of the plant is green, and the kernels are dull grey to brown with white to grayish brown fungal growth on and in between kernels. It usually starts at the base of the ear, and black pycnidia can be produced late in the season.
"The favorable elements for Diplodia are wet conditions during silking," Kelly said. "A wet fall and delayed harvest can promote severe epidemics of it. Bird and insect damage predispose the plants to infection as well."
Kernels tend to be lighter in weight and have reduced nutritional value. With the light weight of the kernels and the cobs, more of them can be ground up when combining, which means higher levels of broken and foreign material.
The good news is there are no mycotoxins in Diplodia corn ear rot.
"For management, the most important source of the inoculum is the debris of diseased corn stalks from previous crops," Kelly said. "Hence, tillage is effective, but if tillage is not practical, less susceptible hybrids and rotation to non-host crops are recommended for Diplodia.
"With all of these, reducing plant stress will help prevent these corn ear rots from forming."