By Doug Schmitz
AMES, Iowa — As of late June, conditions have not had any influence on the development of aflatoxin or other spoilage organisms in crops, according to Greg Brenneman, Iowa State University extension agricultural engineering specialist.
“It is the weather we will have in the rest of the growing season – especially August and September – that will determine if we have mold and toxin issues,” he said.
Brenneman said the prime conditions for the aspergillus (A. flavus) fungus to produce toxins are warm – higher than 70 degrees Fahrenheit – nights during the later stages of grain fill in August-September in a period of drought.
“Any weather conditions that produce lower test weight or damaged grain will decrease the storability of the crop,” he explained. “’Good’ is slightly cooler than normal temperatures with adequate rainfall. ‘Bad’ would be hot conditions that speed up maturity of the crop during the grain fill period and dry/drought conditions in combination with hot weather.”
However, Charles Hurburgh, ISU professor of agricultural engineering, said there is virtually no correlation between weather and toxin accessibility in grain.
“The weather now can’t really be setting the stage for anything,” he said. “August and September are when grain quality is determined. If it’s cool and wet, then we start to think about mycotoxins, which are produced by large fungus in fields. We don’t think of mycotoxins as a storage risk.”
A July 30 Mycotoxin and Crop Report by Lansing, Mich.-based Neogen Corp. stated Kansas and Texas were among the first states reporting mycotoxins in corn for the upcoming harvest season. But there were no additional reports of mycotoxins in winter wheat or barley the previous week.
Clarke McGrath, ISU agronomist and on-farm research and extension coordinator for ISU’s Iowa Soybean Research Center, said at very low dosages – parts per million (ppm) or parts per billion (ppb) – mycotoxins can cause a variety of human and animal health problems.
“In Iowa, mycotoxins are an issue in corn occasionally, but not in soybeans, to my knowledge,” he said. “The better news is that it takes pretty specific conditions for the fungi to proliferate, and even more specific conditions for them to produce mycotoxins.
“So, in other words, the presence of molds does not always mean mycotoxins are going to be produced,” he added.
He said most mycotoxin production occurs in the field before harvest rather than in storage, but poor storage practice can increase already-existing mycotoxin levels.
“In Iowa, we are probably most familiar with aflatoxin,” he pointed out. “It’s more likely to be an issue when maturing corn is under drought stress with prolonged periods of hot weather. Daytime highs above 90 degrees Fahrenheit and nighttime lows above 75 degrees Fahrenheit are the most common figures quoted.
“Fumonisins and vomitoxins are the other two we are relatively familiar with. As opposed to aflatoxin, this group of toxins are believed to be most prevalent with cool, wet weather at grain fill through crop maturity – especially if preceded by any early-season drought stress.
“So as we get into grain fill, we’ll know more about the risk of seeing these show up as well,” he added.
Michael Neary, Purdue University extension small ruminant specialist, said during Indiana’s 2009 corn harvest, mycotoxin levels were high enough to cause concern in livestock. He said the main mycotoxins in feed grains that sheep and meat goat producers need to be concerned with are deoxynivalenol (DON) and zearalenone (ZEN), which arises from Gibberrella ear rot.
He added vomitoxin doesn’t seem to be as much of a problem in ruminant animals as they are in swine. But vomitoxin is also not as big of a concern in sheep and goats as ZEN.
According to a University of Kentucky report, sheep could tolerate 10-15 ppm of DON in total diet dry matter. But a Kansas State University report said a maximum allowable diet dry matter content for sheep and beef cattle during breeding season and for bred females is 5 ppm DON.
Neary said ZEN contamination of feed, however, is a major concern in the breeding ewe. “Modest levels of ZEN in the diet can exert deleterious estrogenic effects on the ewe pre-breeding, which can negatively impact reproductive performance,” he explained.
He said there is less information available about tolerance of DON by meat goats.
“However, since the first sign of DON levels rising beyond a tolerable level is feed refusal, and goats are notoriously finicky eaters, the problem may be self-limiting,” he said. “Combine that with the fact that goat kids aren’t usually finished on the type of high-grain rations that lambs and beef calves are fed.”
To help remedy overall grain toxicity, McGrath advised farmers to consider harvesting aspergillus-infected corn early to minimize more aflatoxin production in the field.
“Holding wet grain for even a short time can allow significant mold and mycotoxin development,” he said. “Visibly moldy corn is not suitable for long-term storage, so prioritize getting it out of storage and finding a ‘safe and legitimate use’ for it.”
Hurburgh said good storage practices in this part of the country will decrease toxicity levels. “We’ll know more (by mid-August) about where we’re going,” he added.
Among other sources of information and references out there on crop toxins, in 2006 the USDA Grain Inspection, Packers and Stockyards Administration published a Grain Fungal Diseases and Mycotoxin Reference guide to compile information, photos and source materials on the data. It is available online at www.gipsa.usda.gov/fgis/publication/ref/mycobook.pdf