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moldy corn
TUNE IN: ISU Extension provides a video and app on managing corn grain infected with mold and mycotoxins.

Identify ear mold, mycotoxin problems in corn

Delayed, wet harvest is raising questions about corn and soybean grain quality and storability.

Wet weather has impacted grain quality this fall across Iowa. With rain delays and a slow start for harvest, a significant number of cornfields have developed ear rots and kernel molds. In addition to too much rain, moderately warm temperatures in September and into October also encouraged mold growth. Likewise, while waiting to be harvested, many soybean fields have developed quality problems and lodging.

“It’s very important to scout each cornfield and identify ear molds that may be present prior to harvesting the field,” says Alison Robertson, Iowa State University Extension plant pathologist.

Proper identification of ear molds can help determine grain handling risks and help farmers develop a plan to limit the impact of the mold on other grain. “You want to isolate the grain that has mold, so it doesn’t contaminate other grain in storage,” she says. “Farmers are being advised to consult their grain merchandiser to find marketing opportunities for moldy grain and to limit the amount of time it is kept in storage.”

If corn has mold, try to get the corn harvested as quickly as possible, says Charlie Hurburgh, ISU Extension grain quality specialist and director of Iowa State’s Grain Quality Lab at Ames. “Once it quits raining and fields are dry enough so you can get back in and resume harvesting, it’s important to first look at some ears in various locations in fields. Identify what kind of mold is out there, if any, to help you determine if there may be a toxin problem.”

Some types of ear molds have potential to produce mycotoxins, he notes. These compounds can have detrimental effects to both humans and livestock if present in food or feed. Field molds normally don’t grow on corn kernels during storage after the corn is dried down to safe moisture content. But holding wet corn in bins and slow drying of the grain in bins can cause mold growth and allow toxins to increase before the corn is dry.

“I can’t emphasize enough that farmers need to avoid holding wet grain in bins or in wagons for very long,” Hurburgh says. “Dry it down to safe moisture content and do it quickly.”

Properly identify molds, mycotoxins
With all eyes now on harvested grain quality and scouting fields for mycotoxins resulting from ear rot this fall, it's important that producers and agronomists have access to practical information on this topic, on whichever medium they prefer to use. ISU specialists developed a YouTube video to help.

The Mycotoxins app is also available on both Android and iOS to serve as a guide for navigating the sometimes confusing world of grain quality issues. The free app presents important information about different corn ear rot pathogens that cause major yield losses. In addition, the app provides instructions and tips that are valuable for corn farmers and livestock producers for a proper management plan for corn infected with mycotoxins.

The app presents information about symptoms and mycotoxins produced by predominant corn ear rot pathogens, toxic effects of mycotoxins on humans and livestock, and safety levels for different uses of infected grain. The app also provides tips on storing moldy grain, ear rot management before and during harvest, and scouting and testing corn for mycotoxins.

Critical management steps to take
Stalk strength in cornfields is deteriorating, so there will be more downed or broken stalks. “Harvest the downed corn first, regardless of moisture content because mold growth is accelerated, and drydown rates for corn in the field are reduced,” Hurburgh says.

The two most important steps this fall are:
• drying corn quickly without long holding periods
• cooling corn as quickly as possible once it’s in a storage bin after drying it to safe moisture content

“You don’t want to be holding wet corn too long — in wet holding bins or wagons or whatever,” he cautions. “It will spoil much more rapidly than we would normally experience with drier corn. This fall we want to be drying corn as fast as possible.”

Cool corn to 40 degrees or below
If you can’t dry corn as soon as you harvest it, in either a continuous flow dryer or in an airflow drying bin, the grain isn’t going to keep very well, especially in wet weather. “The key is to get that corn into the bin at a cold temperature, and I think we’ll have a chance for that,” Hurburgh says. “When it’s 40 degrees [F] or below, every fan in Iowa should be turned on and running to get as much of this grain as cold as we can as soon as possible.”

What would be the ideal temperature to cool the corn? “We like to get the grain below 40 degrees,” he says. “I don’t know if we’ll be able to do that this fall. It’ll depend on the dewpoints. The weather was warm and wet into mid-October, warm for that time of year. And those are the conditions that generally produce mold on ears in the field and the toxin issue.”

Grain buyers look for toxins
Grain elevators are looking closely at corn samples pulled from loads coming in this fall. Some are running a blacklight test. A blue-green glow from corn under a blacklight is somewhat correlated with the presence of aflatoxin.

“I don’t think we’ll have many aflatoxin problems this fall, so I don’t think the blacklight test is going to show us much,” he says. “While the glow under a blacklight can be an indication of aflatoxin in corn, it’s not highly correlated. But at least it gives you an idea of whether the risk of aflatoxin is there.”

What about vomitoxin? That’s the toxin Hurburgh thinks will present the most problems with this fall’s corn harvest. “For detecting vomitoxin, a blacklight test doesn’t do anything,” he says.

The only way to determine whether corn has a risk of producing vomitoxin is to conduct a strip-test on a sample. “A grain buyer could do this twice a day to determine if corn in the area might have a vomitoxin problem,” Hurburgh says. “Some grain elevators are doing this testing.”

There’s no rapid way to tell if corn will produce vomitoxin. “If you see mold that looks like a white sheath growing on the corn kernels on the ear, if it is white from the tip of the ear on down, that’s the Gibberella fungus that can produce vomitoxin. That’s the tipoff, indicating maybe this corn should be tested with the strip test. If you are feeding your own corn to livestock, get it tested,” Hurburgh says.

Ethanol plants concerned
Ethanol plants are worried about vomitoxin possibly being in corn they receive. In Iowa, a large amount of the distillers grain produced by ethanol plants is fed to pigs, and pigs have the lowest tolerance for vomitoxin compared to cattle or other livestock. Pigs are the most sensitive to vomitoxin.

An ethanol plant, when fermenting corn and processing it to make ethanol, will concentrate by a factor of 3 anything other than starch that comes in with the corn. So, if the toxin comes in with corn to the ethanol plant, it comes out of the ethanol plant with three times as much toxin in the distillers grain. If you start with 1-part-per-million vomitoxin in the corn, the dried distillers grain produced will be 3 ppm.

“That’s why ethanol plants are concerned,” Hurburgh says. “They have a 3-to-1 concentration factor. If you are feeding corn that came from the same area that produced corn for the ethanol plant, you could have two sources of vomitoxin in the same hog ration: the corn and the distillers grains.”

Summing up
Don’t hold wet corn; get it dried down right away. If you can’t do that, then run cold air on it and get it cooled down as fast as possible. Controlling grain temperature is the fastest way to slow down mold growth in grain, Hurburgh says.

Drying corn as quickly as possible means running grain bin dryers at their maximum temperature. “And using a continuous flow, high-temperature dryer is even better because they dry faster than bin drying systems,” he notes.


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