By DOUG SCHMITZ

Iowa Correspondent

AMES, Iowa — While mycotoxins have been reported sporadically – and are not commonly a problem – in soybeans, plant pathologists and agronomists do have to be attentive to corn since it is suitable for many fungi, including those that can produce different mycotoxins.

“Aflatoxins are one class of mycotoxin that tend to be associated with hot drought conditions during pollination and grain fill,” said Erin Bowers, Iowa State University associate scientist. “Iowa occasionally has aflatoxin problems and in any given year, you may be able to find a sample or two collected in the state that tests positive for aflatoxin.

“It is typically the broad-scale contamination of the grain supply that we becomes problematic because it becomes difficult to identify and target grain at various levels of contamination to go to end users that can safely make use of it. This is true of any mycotoxin contaminating our grain supply.”

Last year, she said dexoynivalenol (DON), which is known to many as vomitoxin, was “our mycotoxin problem.

“There was a low level of contamination with DON, which affected grain produced across most of the state of Iowa,” Bowers explained. “This did cause some issues. Swine are sensitive to DON. The persistent, low-level contamination in corn in their diet, coupled with inclusion of other locally-sourced, grain-based ingredients (i.e., distillers dried grains) meant a good portion of their diet was contaminated.

“The process of making fuel ethanol from corn concentrates mycotoxins three times what was in the original corn, so our swine last year was at risk last year of some negative health and production effects from DON exposure.”

This year, she said the risk remains to be confirmed, but based on reports of specific types of ear molds from extension field specialists, “we suspect fumonisins may be an issue in the state. Additionally, in the southeast quadrant of the state, there may be ochratoxin A problems.”

The U.S. Food and Drug Administration does not currently have published guidance levels for ochratoxin A in feed, but negative production and health effects have been documented in poultry and in livestock species (including swine).

Regarding storage, Bowers said mycotoxins don’t affect how grain will store, but grain conditions going into storage can affect the risk of mycotoxin levels increasing during storage. “We anticipate high variability in grain this harvest, which can make it difficult to dry, and it will not dry evenly.

“Grain that is pocketed with high moisture spots will likely generate ‘hot spots’ of continued spoilage and mold growth during storage (this continued mold growth may result in continued production of mycotoxins, depending on the predominant fungal species and other factors),” she added.

To the extent possible, she said farmers need to reduce the variability of harvested grain “batches” by being attentive to hybrid differences, re-plant areas, and other sources of variation within fields.

“Mycotoxins also tend to be associated with fines, and with broken and lightweight kernels,” Bowers noted. “Removing bin cores takes out much of this type of grain, which improves airflow in bins and may also improve the overall quality and prevent additional mycotoxin issues in the remaining grain.”

Nathan Kleczewski, University of Illinois Urbana-Champaign research assistant professor and extension pathologist, said diseases were not a major issue in Illinois this season and only some pockets of fields in parts of the state suffered from fusarium head blight (FHB) at levels that resulted in DON contamination and reduced yields.

He said successful management of FHB must include an integrated approach. “No single management strategy will be effective at reducing yield loss and vomitoxin contamination in a disease-favorable environment,” he said.

“We cannot completely stop damage from FHB, but we can suppress its effects and reduce yield damage. The first and most important tool growers have in their toolbox is the use of a variety with moderate resistance to FHB.”

Kleczewski said varieties with moderate resistance to FHB will have reduced yield losses, compared to susceptible varieties, and will help reduce vomitoxin contamination in the grain.

“As we are all aware, if the vomitoxin content in the grain exceeds the maximum acceptable levels, the grain will be docked or deemed not be acceptable for sale,” he said. “My goal as an extension plant pathologist is to help producers effectively manage FHB so that the vomitoxin levels in their grain is below the acceptable thresholds, allowing for the sale of their grain.”

Virgil Schmitt, ISU field agronomist for southeastern Iowa, said it’s too soon to tell what effect mycotoxins will have on grain this fall since there hasn’t been much harvesting done in his area yet.

“I have received one report of a load of corn being rejected by an ethanol plant in south-central Iowa due to aflatoxin,” he explained. “I do see quite a few ear molds in the corn fields, so mycotoxins may be an issue as harvest gets going.

LAST YEAR, VOMITOXIN was the mycotoxin problem. The FDA does not currently have published guidance levels for the mycotoxin ochratoxin A, shown here in feed, but negative production and health effects have been documented in poultry and in livestock species, including swine.

(Courtesy of Alison Robertson)