Grain, Stalk Quality Concerns Increasing

By Jane Fyksen, Crops Editor
Thursday, October 25, 2007 11:09 AM CDT

Aspergillus flavus

Reports of mold and lodging in corn are widespread across Wisconsin, according to the Wisconsin Agricultural Statistics Service, that noted on Monday that corn harvested for grain was 38 percent complete, though still ahead of last year’s 25 percent and the five-year average of 30 percent in storage.

At Agri-View’s press deadline, UW-Madison corn specialist Joe Lauer hadn’t yet confirmed the predominant type of mold on Wisconsin corn, though he, too, said there’s “quite a bit” out there in unharvested fields.

Rainfall over the past two weeks has slowed harvest progress. Earlier this week, soil moisture levels were rated 53 percent “adequate” and 46 percent “surplus” with only one percent “short.” The condition of the corn was rated by producers as: 8 percent “very poor,” 13 percent “poor,” 36 percent “fair,” 33 percent “good” and 10 percent “excellent.” There were even reports of corn sprouting on the cob in northern areas of the state.

Lauer, like Agri-View, was hearing rumblings about aflatoxin, a serious mold-related concern, and one that’s typically a southern Corn Belt problem. Aflatoxin has been confirmed in corn in northwest Iowa and southeast South Dakota. That far north is “unusual,” said Lauer.

Iowa’s Ag Secretary Bill Northey has been reassuring farmers about the discovery of aflatoxin in his state, saying that the necessary steps were being taken to handle it. The discovery was not “completely unexpected,” he noted, and “shows that elevators are prepared for it and taking the necessary precautions to make sure affected corn is used appropriately,” Northey said last week.

Heavy rain that followed hot, dry weather this year has made a fertile breeding ground for aflatoxin - poisonous, highly carcinogenic byproduct associated with Aspergillus. It can also spread once corn is in the bins if conditions are conducive, especially at moisture content over 12 percent and temperatures greater than 70 degrees.

Aspergillus has the potential under drought stress and insect damage to produce aflatoxin. Aflatoxin can be produced in standing grain before harvest. Aflatoxin, once produced, is quite stable to heat, milling, pelleting and many chemicals. While four specific aflatoxins are generally produced (designated B1, B2, G1, G2), the most frequent and toxic is B1.

“The levels it’s being found at are not especially high and there is a lot of corn that it can be blended with to make sure it won’t cause any problems when fed to livestock,” Northey said. “I think it’s important the public knows we’re aware of the situation and taking the necessary steps to make sure it doesn’t cause any health issues for animals or humans.”

High moisture conditions favor growth of many ear and stalk rot fungi, increasing the risk of ear rots and mycotoxin contamination. Field damaged corn, regardless of the reason, shouldn’t be mixed with good grain. Damaged or low test weight grain must be aerated immediately to reduce temperature and equalize moisture. Field damaged corn won’t store beyond the winter months. Maintain 1 to 2 percentage points lower moisture than normal grain (13 percent corn, instead of the most typical 15 percent). Again, if growers suspect mycotoxin problems, check with your crop insurance provider to see if adjustments may be needed and how to represent areas to be adjusted. Crop adjustments for quality problems, including mycotoxins, must be done on standing corn at or before harvest.

Ears on some hybrid stay upright and/or have open husks. Upright ears and open husks can serve as funnels and receptacles for water. Given enough moisture and warm temperatures, corn on the ear will germinate, as is reported in places in Wisconsin, reducing grain quality.

With the persistent damp weather, some growers have noticed a change in the color of plant tissue, described as blackish soot. A sample brought to the Iowa State University lab contained this black growth. It was primarily due to a fungus, Alternaria, although there were likely other fungi present (including Colletotrichum), report ISU experts. Alternaria is a common decay fungus, which decomposes dead organic matter. Although Colletotrichum is often a pathogen earlier in the growing season, it’s also a common organism that feeds on decaying dead organic material late in the season. This discoloration of plant tissue won’t affect grain yield or quality, yet it will likely increase stalk degradation.

Aflatoxin should be on radar

Aflatoxin, which, as noted, isn’t necessarily a concern in Wisconsin’s moldy corn this year, is harmful or fatal to livestock when consumed in high quantities and, as noted, considered carcinogenic to humans. As a result, elevators have been testing loads received from at-risk areas.

Ethanol plants also do some testing so they ensure they are not buying corn with aflatoxin, which, Lauer said, can concentrate in the distillers grains, a co-product of ethanol production and feed supplement for livestock.

“This is a lot bigger deal than some people want to believe,” said Roger Price, general manager of Farmers Cooperative in Hinton, Iowa. Price said the co-op’s elevators in several Iowa counties have rejected corn that has more than 20 parts per billion of aflatoxin.

Experts recommend farmers inspect their fields for the gray-green mold, especially in areas that are more stressed from drought conditions. The mold may be present in only part of a field. If they check before harvesting, producers could collect crop insurance.

“If they discover this when they’re hauling it to the grain elevator, it’s too late,” warned Joel DeJong, an Iowa State University crop specialist. “They’re not going to cover you.”

DeJong added anyone combining tainted fields should wear a mask to prevent inhalation of aflatoxin, which is a carcinogen.

Lauer, however, wanted to make it very clear that just because there’s mold on corn doesn’t automatically mean there’s aflatoxin, or mycotoxin for that matter, which he noted, is typical “every year” on some corn in Wisconsin. Mycotoxin is associated with the Fusarium/Giberila complex of mold.

“Just because you have mold doesn’t mean you have toxin,” Lauer stressed. Nonetheless, he recommended producers send samples for final determination into the UW’s Plant Disease Clinic in Madison, first calling 608-262-2863 about the submission and the necessary tests. Lauer said they’ll need to identify both the mold, and whether a toxin is present n and at what concentration. Toxin-contaminated corn can be fed, he notes, if it’s diluted out with healthy grain.

Early testing at elevators or other collection points is often done in two ways. A “black light” (ultraviolet light) illuminating aflatoxin-contaminated grain causes a firefly-like greenish-yellow fluorescence which is caused by a non-aflatoxin product that results from growth of the Aspergillus specie of mold. This is not aflatoxin, but serves as a marker that aflatoxins may be present. Overall, this test is subject to inaccuracy of around 13 percent and in some locations can result in as much as 25 percent incorrect answers. This technique should not be used to measure the amount of aflatoxin in the grain. A rational decision about use of grain cannot be made on the basis of the black light alone, according to Iowa State University.

The second method involves quick tests based on chemical or antibody detection of aflatoxin itself. These tests require some basic chemistry to conduct, but are often conducted on-site or in laboratories nearby where grain is collected. They are generally useful and can give approximations of the amount of aflatoxin in a specific sample. Some commercial and state labs also offer full service chemical and instrumental testing to confirm and quantify aflatoxin. Testing is only accurate if a representative sample is collected. Sampling is an estimate and inattention to sampling technique can cause large errors in results. Because aflatoxin can vary widely in a field or storage bin, some specific sampling techniques are strongly recommended. Thus Lauer suggested growers call the UW lab first for advice.

According to Iowa State University, field sampling is difficult and subject to inaccuracy. A suggested method for collecting a field sample is to make one or more trips across a field with the combine. Then, as the hopper is emptied into a wagon, pass a cup through the stream of grain every 30 seconds and collect these to make a total of 10 pounds or more. Mix the collected sample thoroughly and submit as least 5 pounds for testing. If the field is large, sample several times at different locations across the field. Sampling ear corn is less accurate, and if this is done at least 30 to 50 sites with several ears per site should be collected.

Moisture content of samples to be tested should be less than 14 percent for short term shipping to a laboratory. If grain moisture is higher, seal the bag, freeze the grain and keep it cold until it reaches the laboratory. An alternative is to dry the grain for 6 to 12 hours at 140 degrees, then ship to the laboratory in a paper bag.

Sampling from stored grain should be done by the moving stream method as described above for sampling from a combine. Probe sampling is acceptable where grain has been recently blended. Multiple samples (10 to 30) from several levels of the bin should be sampled. Never trust a “grab” sample as representative of the entire grain supply.

Effects of aflatoxin on livestock

Small amounts of aflatoxin cause mild or negligible effects and larger amounts cause increasingly serious effects. Low levels in feeds - sometimes less than 1 part per million (ppm) n can cause poor growth, interfere with the immune system and result in liver damage and bleeding. High dosages cause acute loss of appetite, depression, hemorrhage, diarrhea and death. Signs of aflatoxin poisoning can include slow growth, reduced milk production, hemorrhage and jaundice (yellow color of skin and eyes). With continued exposure, there will be liver damage and suppression of the immune response and ability to resist infections or to respond adequately to vaccinations.

Animal susceptibility varies with species and age. In general, young animals are more affected than adult animals. Species that are highly sensitive are trout, ducks, turkey poults and pre-weaning pigs. Animals that are moderately sensitive include all swine, growing turkeys, broiler chicks, pre-ruminant calves, dogs and horses. Animals most resistant are beef feedlot cattle, open cows, and sheep.

Aflatoxin generally does not interfere with fertility or cause abortions. However, newborn animals nursing dams that consume aflatoxin can be exposed via milk.

Aflatoxin is excreted rapidly from the body, so detectable levels may be gone within a few days to one to two weeks. Complete laboratory submission for diagnosis should include suspect grain or feed, fresh liver and kidney, urine if available, serum for laboratory tests of liver function and rumen or stomach contents.

FDA (Food and Drug Administration) guidelines have established “action levels” for acceptable concentrations of aflatoxins in specified foods and feeds (http://vmcfsan.fda.gov/~lrd/fdaact.html). The following levels from FDA are presented for information purposes. Keep in mind these may change, and one should always check directly with FDA or appropriate state authorities to verify acceptable levels. Here are FDA guidelines (fed to food animals, commodity amount): corn for interstate movement, 20 parts per billion (ppb); corn for all dairy animals, 20 ppm; milk, 0.5 ppb for fluid milk; corn for finishing swine over 100 pounds, 200 ppb; and corn for finishing beef cattle, 300 ppb.

Aluminosilicate products such as hydrated calcium aluminosilicate (HSCAS) and sodium bentonite have proven effective in binding aflatoxins and preventing their absorption. Usually they are added to feed at 5 to 10 pounds per ton. They have been shown to reduce effects of aflatoxins on the liver and to reduce aflatoxin residues in milk. Recently modified glucan based adsorbents have also been developed and marketed (Mycosorb, Alltech). They may be similarly effective as the aluminosilicates and are used at lower levels in feeds.

Affected animals should be given high quality protein supplements. In addition, although vitamin E and selenium do not appear to protect against aflatoxins, vitamin E may be depleted in mold contaminated feeds and testing for its status in animals or supplementing the ration is recommended.

Mold inhibitors, such as the organic acids, can prevent continued mold growth where moisture above 12 to 14 percent is a problem. Mold inhibitors prevent mold growth, but do not destroy or modify aflatoxins.

Treatment of grains with anhydrous ammonia for 12 to 14 days reduces aflatoxin content, but regulations vary from state to state about the clearance of ammoniation for contaminated corn.

The two primary mycotoxins affecting corn are aflatoxin and fumonisin. Fumonisin is produced by the Fusarium family of molds, similar to Fusarium ear rot. Fumonisin is highly toxic to some species, especially horses. Other mycotoxins, such as Citrinin, Cyclopiazonic acid, Penicillic acid, Deoxynivalenol (DON or vomitoxin), Ochratoxin A, Zearalenone, and Trichothecenes (T-2) may also affect corn, according to the National Corn Growers Association.

Again, Lauer cautioned producers not to immediately jump to the conclusion that aflatoxin is present in moldy corn. However, the longer corn remains in the field, the greater the chance of toxin production. To minimize losses due to ear rot and increased mycotoxin levels, producers should harvest problem fields as soon as possible n of course, easier said than done.

Toxins of most concern typically in Wisconsin to increase in the field at this time are the Fusarium-based toxins, vomitoxin and fumonisin. Adjust equipment to minimize damage to kernels since mold and mycotoxin levels tend to be greater in damaged kernels. Dry (less than 15 percent moisture) and cool (under 45 degrees) grain as quickly as possible to reduce further mold growth and toxin production.

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