It seems like a broken record for Iowa's corn harvest this fall...weather changes have shifted expectations of new crop corn quality. Three weeks ago, somewhat wetter corn than normal but high quality was the forecast. It is clear that the wetter part will come true; early harvest moistures are generally coming in at 18% to 22% corn moisture content, which is above average but not high enough to cause severe complications in drying. "Field drydown is probably nearly over so do not expect much change in grain moisture from here on, as the corn stands in the field," says Charlie Hurburgh, an Iowa State University grain quality expert and director of the Iowa Grain Quality Initiative.
Overall quality has been put at risk however, in some areas of Iowa, says Hurburgh. The mid-September frost in far northern Iowa caused more reduction in grain fill than was previously thought. This is showing up as lower test weight. This issue is more prevalent in Minnesota, Wisconsin and northern Illinois. The rest of the state of Iowa still is seeing test weights of 57 pounds per bushel and up, after the corn is dried.
If you have some frost related issues, Hurburgh suggests you read PM1635, Frost Damage to Corn and Soybeans.
Wet weather in areas of Iowa has increased risk of field molds
The southern half of Iowa (see map below) this fall has had extreme rains in late September into October. This will raise the chances of field molds, primarily Gibberella, but Fusarium may also be present, says Hurburgh. Both of these fungi produce toxins. The most likely will be deoxynivalenol (vomitoxin), others include zearalenone (often found with vomitoxin) and fumonisin.
Examples of affected ears and recommended feeding limits are given below. None of these toxins are regulated by the federal Food and Drug Administration, but guidance or advisory level recommendations have been issued as a result of the negative health impacts they can have on livestock that consume them.
Photo A: Gibberella Ear Rot – This mold produces deoxynivalenol (vomitoxin) and zearalenone
Advisory Levels for Deoxynivalenol (Vomitoxin) in Livestock Feed
Zearalenone causes estrogenic activity in swine and dairy that manifests as reproductive effects.
• Negative effects on cattle: infertility; reduced milk production; hyper-estrogenism
• Negative effects on swine: enlarge mammae; swelling of uterus and vulva; atrophy of the ovaries; withered testes
There are no FDA action, advisory, or guidance levels for Zearalenone.
Photo B: Fusarium Ear Rot- This mold produces fumonisins
Guidance Levels for Total Fumonisins in Livestock Feed
Scout cornfields before harvesting them, look for molds
The best action is preharvest scouting of cornfields, says Hurburgh. Once harvested the presence of the fungi and subsequently the risk for toxin contamination is more difficult to assess. If ear rot is present on more than 10% of the ears in a field, that field should be scheduled for harvest sooner. Harvested grain should be dried to less than 15% moisture and cooled immediately to prevent further growth of the mold and production of toxins. Affected grain should be stored apart from non-affected grain.
Affected corn fed on farm should be tested; your veterinarian can access the Iowa State University Vet Diagnostic Lab. Official USDA-GIPSA grain inspection agencies can also test for these toxins. Provide at least 10 lbs. of sample taken from multiple points in the grain lot.
Feed and processing markets are probably monitoring for toxins on a periodic composite sample basis. Testing every incoming load is not very practical except in extreme conditions. The tests for these toxins are generally immunoassay-based strips that take about 10 to 15 minutes to run and cost about $10 to $15 per toxin.
Overall the risk of toxins in 2014 corn isn't clear yet
In Iowa the highest risk areas for toxins will correspond to the areas with highest rainfall during harvest, he says. This makes occurrence spotty with rainfall patterns.
Overall the risk of toxins in 2014 corn is not yet clear, but the wet conditions have increased the possibility of vomitoxin, zearalenone, and fumonisin. Aflatoxin is not a threat in Midwest corn this year. Grain buyers should monitor composite samples to identify potentially high risk areas. If mycotoxin levels in composite sample tests exceed about 40% of the limit for a specific toxin in composite samples, stored grain will likely have pockets of contamination above recommended feeding levels for certain livestock.
He says the best practice would be to increase testing frequency in order to either reject or isolate highly contaminated lots at the point of delivery for use in feed for livestock that have a higher tolerance.
Visibly moldy grain, at levels sufficient to create a price discount for damage, may not be present in all corn samples that have toxins, notes Hurburgh. Grain fed from fields showing the presence of fungi should be tested before use.
Contributing to this article: Charles Hurburgh is a professor in the Department of Ag and Biosystems Engineering. He can be reached at 515-294-8629 or e-mail [email protected]. Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology; she can be reached at [email protected] or 515-294-6708. Erin Bowers is a post-doctoral research associate in the Department of Agricultural and Biosystems Engineering. She can be reached at [email protected] or 515-294-6383.