Farmers just can’t catch a break this season. After coping with the most difficult spring planting conditions in recent memory, challenges continue as we approach late season.
Maturity of the 2019 corn crop is all over the board given staggered planting dates as farmers dodged rain and wet conditions. The few fields planted during late April and early May experienced very hot, dry conditions during pollination.
Conversely, fields planted more than a month later, during early June, benefited from cooler conditions during pollination but are well behind in maturity.
Given the variation in weather across the state, farmers are likely to observe a wider variety of ear molds this year.
Additionally, with corn earworm out in full force, there is a greater opportunity that farmers may experience an increased incidence of ear fungal diseases.
Corn earworm feeding creates easy entry points for diseases of the ear. Early signs of ear rot indicate corn harvest may be troubled with some level of molds, although it is still too early to predict the severity of damage.
Several pathogens causing ear molds usually infect the plant from pollination to 21 days after silking. The primary infection point is through the silks and into the ovule or developing kernel.
Several mold pathogens thrive in warm and wet weather conditions, while others are more common in hot, dry environments. Although infection occurs early, symptoms do not usually appear until R5, or dent.
When evaluating ear molds, it is important to understand and identify which infections have developed.
Common Ear Molds
Diplodia, gibberella and fusarium favor wet weather with heavy morning dew and humid days. Initial infection of diplodia ear rot appears at the base of the ear with a white-colored fungus.
As the disease progresses, the mold and kernels turn grayish or grayish-brown and may rot the entire ear. Although it does not cause mycotoxins, it can reduce grain test weight and can result in significant docks at the grain elevator.
Gibberella ear mold, distinguished by its pink to reddish color, begins at the top of the ear and, in highly susceptible hybrids, can affect the entire ear. Gibberella does produce mycotoxins, vomitoxin and zearalenone, so the grain must be handled separately and tested for contamination.
Fusarium, the most common of all ear molds, is distinguished by the white to light pink-colored fungus appearing on scattered kernels, especially those damaged by insects.
Fusarium infects the corn ear in patches or on single kernels. The kernels turn tan or brown, and the mold appears to be white, gray or pink in color.
One of the three species of fungi causing fusarium ear rot also produces mycotoxins. Because the symptoms for all three species are similar, a lab test is needed to identify the infecting fungus.
Less Common Ear Molds
Trichoderma and aspergillus ear molds are less commonly observed but may be found in fields this year. Trichoderma is a thick green mold that grows on and between kernels.
The species infecting this area do not produce mycotoxins but will affect grain quality. Incidence tends to be associated with damage, whether by birds, insect feeding, or mechanical injury.
Aspergillus features a gray-green powdery mold and occurs in hot, dry years. It produces a mycotoxin, known as aflatoxin, so the corn should be handled separately and tested.
Accelerate harvest if needed. There is no rescue treatment for ear molds, so it is important to identify fields with the highest levels of the disease and harvest those first.
Ear molds will continue to develop in the field even after the corn reaches physiological maturity and begins to dry down. Even after corn is harvested, molds will continue growing until the grain is dried to 13% to 15% moisture.
If weekly scouting is a challenge on your farm, work with your local Mycogen team or retailer to prioritize scouting by hybrids.