Varying weather elements, late planting and larger thresholds of corn earworm and other damaging insects after silking have left many growers with corn ear molds in their fields. Ear molds can lead to harvestability issues for a few reasons, so growers need to be able to recognize the signs of ear mold in their fields and determine which mold they are dealing with. Here are the four main ear molds to watch for this fall.
Diplodia: Diplodia is one of the most common ear molds growers are finding in their fields this fall. Diplodia is white to gray in color and usually begins at the base of the ear, growing between kernels. Black spots can often be spotted on the husks and even on stalks. Diplodia usually starts growing about two weeks after silking and can greatly impact grain quality and, ultimately, yield. Diplodia can also cause stalk rots.
Aspergillus: Typically gray-green to light green in color, aspergillus mold starts at the tip of the ear. Damaged kernels caused by insects or hail earlier in the season give this mold a site to enter and begin growing. Nitrogen deficiencies can also cause this mold. Aspergillus can form aflatoxins, which are poisonous carcinogens that can become toxic to livestock and humans.
Gibberella: Gibberella can be detected by its bright pink to red or even white color. It’s typically present on the tips of ears, but it can also be detected on the stalk, causing stalk rot. Gibberella favors cool and wet weather after silking. Earworm damage is a good point of entry for gibberella mold to form. Gibberella can also form vomitoxin, a form of mycotoxin that is harmful to livestock such as hogs, even with only five to 10 percent of ear rot present.
Fusarium: White to pink in color, fusarium usually starts at the tip of the ear and can cause stalk rot. Infection starts where kernels crack during growth or when ear damage from insects is present. Fusarium thrives in warm and dry weather, and can form fumonisins, a group of mycotoxins that are toxic to livestock.
Damage Potential
Damage potential is greatest for all these molds from silking to harvest, especially with the excessive rainfall we’ve had this year. We’re also seeing a lot of ear molds where large amounts of insect feeding from ear worms, aphids and corn borer occurred this summer. This situation is more common in fields where conventional or straight Roundup hybrids were planted. We’re also seeing more damage in areas where late planting, excessive heat at pollination and an early frost before black layer occurred, leading to underdeveloped kernels with lighter test weights. Growers need to watch for areas of lighter test weights, as they may be a strong indicator of ear mold presence.
As referenced above, ear molds can also develop toxins that are dangerous for animal consumption. Some animals are more sensitive to toxins, such as hogs and dairy cattle. There are different types of mycotoxins that form based on the ear mold, which is why it’s important to detect the mold before harvest and get it tested before taking it to the grain elevators.
If growers suspect they have an ear mold infestation, it is recommended to test several locations in their fields, pulling anywhere from 10 to 20 ears in each location. If they run into higher thresholds of affected ears, management tactics must be implemented. The Ohio State University’s Agronomic Crops Network recommends, “If you have damaged ears and moldy grain, get it tested for mycotoxins before feeding to livestock, and if you absolutely have to use moldy grain, make sure it does not make up more than the recommended limit for the toxin detected and the animal being fed.” The U.S. Food and Drug Administration has established maximum allowable levels for mycotoxins and other toxins in corn, which should be properly adhered to.
Management and Prevention
Growers experiencing ear molds this fall need to consider a few management tactics for harvest this season and for the coming years. Grain storage and proper drying will be important in fields with a high incidence of ear mold this fall. Ideally, we would like it to dry down in the field as much as possible to avoid down corn. Make sure your combine is set to minimize even more kernel damage than is already present. Test weight is more than likely going to be lower this year, which means you may be at higher risk of kernel breakage with handling and a shorter storage life. The University of Wisconsin Crop Manager recommends storing contaminated corn separately as the fungi can grow on good corn during storage.
Growers trying to decrease their chances of getting ear molds in the coming years need to consider a combination of crop rotation, deeper tillage and planting hybrids such as -20 or Agrisure Duracade® for better insect protection from pests like the western bean cutworm, corn borer and earworms. Stine has a number of great options in these categories for the 2020 growing season. Growers also need to consider a good fertilizer program to avoid plant stress.
For more information and recommendations on corn ear molds this harvest, contact your local Stine agronomist or university extension office.
Resources and Citations
Ear Rots of Corn: Telling them Apart
https://agcrops.osu.edu/newsletter/corn-newsletter/2018-28/ear-rots-corn-telling-them-apart
Corn Earworm in Field Corn; Watch for Molds
https://agcrops.osu.edu/newsletter/corn-newsletter/2019-27/corn-earworm-field-corn-watch-molds
Corn Stalk Rots and Ear Rots
https://ipcm.wisc.edu/download/wcm-pdf/WCM2019/WCM2019_22b.pdf