By Matt Reese and Dale Minyo
Corn harvest is wrapped up for Ohio, but challenges from vomitoxin in the 2020 crop have been lingering.
The problem got its start with the fairly widespread development of Gibberella ear rot (GER) in corn around Ohio. Ohio State University Extension plant pathologist Pierce Paul said GER development is favored by warm, wet, or humid conditions between silk emergence (R1) and early grain development.
“Unfortunately, slow dry-down coupled with delayed harvest, late-season rainfall, and/or high humidity, and warmer-than-usual late fall are responsible. Unlike the leaf diseases that you can see just by walking plots, ear diseases may go undetected, unless you peel back husks and check,” Paul said. “The fungus usually gets in during silking, then grows and produces vomitoxin as the grain develops. Weather conditions during grain-fill and that pre-harvest window determines how bad it gets. I have heard as much as 5 to 10 parts per million in the odd field, but levels between 2 and 5 ppm have been reported as well.”
GER leads to grain contamination with mycotoxins, including deoxynivalenol, which is also known as vomitoxin. Once vomitoxin is present, it requires management. Paul said proper storage is key. Warm, moist pockets in the grain promote mold development, causing the grain quality to deteriorate and toxin levels to increase. Proper aeration is important to keep the grain dry and cool. And,
while cool temperatures, air circulation, and low moisture levels will minimize fungal growth and toxin production, these measures will not decrease the level of toxin that was already present in grain going into storage.
Paul suggested the following tips for handling corn with vomitoxin on the farm.
- Dry and store harvested grain to below 15% moisture to minimize further mold development and toxin contamination in storage.
- Store dried grain at cool temperatures (36 to 44°F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.
- Periodically check grain for mold, insects, and temperature.
- If mold is found, send a grain sample for mold identification and analysis to determine if toxins are present and at what level.
- Clean bins and storage units between grain lots to reduce cross-contamination.
Several aspects of the 2020 growing season set the stage for the problem, said Luke Schulte, CCA, Beck’s Hybrids Field Agronomist.
“Most GER enters the ear via the silk channels after pollen shed has ceased. Heat or drought conditions during pollination that cause a lack of kernel fertilization will make it worse. Then we get some moisture post-pollen shed and unfertilized ovules’ silks elongate, but there is no pollen to then compete or collect on the silks. Late-planted corn is typically more impacted due to the shorter days throughout grain fill,” Schulte said. “One reason we are now hearing of more, although we knew of some throughout harvest, is much of the grain harvested is stored on-farm. Many growers only dry their corn to approximately 16% to 16.5% and then rely on fans to remove the rest of the moisture after storage begins. GER can continue to grow to approximately 15% moisture. We are hearing of more issues now for two additional reasons. First, many growers weren’t aware while filling the bins of a problem and are now just beginning to haul back out. Also, while in harvest grain terminals often do not test for VOM.”
The problem that got its start during the growing season has been showing up in full force at grain elevators around the state in recent weeks. Craig Haugaard, vice president of grain for Sunrise Cooperative said vomitoxin has been a significant challenge in 2020 corn.
“We have seen it throughout our entire trade area. There were certain sections that were maybe a little worse than others but we have seen it very widespread this year. I have talked to folks in the grain testing business and they’re saying they’re seeing it throughout the state of Ohio. I think it is something everyone will have to deal with at some level this year,” Haugaard said. “There may be some uniquely defined markets shake out this year. I wouldn’t be surprised to see a premium market for low-VOM corn and a market for the higher VOM stuff that is more limited in usage. We start doing daily composites at the start of harvest and we are at levels now where by in large we are limited in where we can go with it. That is pretty typical for a large part of the state of Ohio.”
The problem seemed to get worse later into harvest.
“It was almost a tale of two harvests. Early on the corn coming in had some vomitoxin in it but not at levels that were alarming. Then we had that extended rain period and people weren’t getting out in the fields for a couple of weeks,” Haugaard said. “As soon as we started back up we noticed the vomitoxin really accelerate. If you got it in early you probably didn’t have as much of a problem as if you harvested later this year.”
Ultimately, vomitoxin is a problem when the corn is used for feed.
“Vomitoxin, or deoxynivalenol (DON), is a secondary metabolite or mycotoxin produced by Fusarium molds that can cause health and productivity issues in livestock,” said Erika Lyon, Agriculture & Natural Resources Educator, Ohio State University Extension Jefferson/Harrison counties. “Some livestock species, such as swine, are more sensitive to DON, while ruminants can typically transform the toxin into a less toxic product as it passes through their digestive tract, due to their rumen microbes. However, age and immune status among other factors can play a role in determining an individual’s sensitivity to the toxin as well.”
Symptoms of vomitoxin consumption by livestock include, as its name suggests, acute temporary nausea and vomiting, along with fever and other immunological and productivity issues.
“Livestock may also refuse contaminated feedstuffs. Feed refusal, ketosis, reduced milk production, diarrhea and displaced abomasum can occur at levels as low as 1.5 to 2.5 ppm of the total ration dry matter for cattle, even though ruminants are less sensitive to vomitoxin compared to non-ruminants such as swine,” Lyon said. “Grains exceeding advisory levels can be diluted with uncontaminated corn and other feedstuffs during rationing to reach the diet percentages. Keep in mind that DON also becomes more concentrated in distilled by-products.”
The Food and Drug Administration has set the following advisory levels for vomitoxins (on an 88% dry matter basis):
- For ruminating beef and feedlot cattle over 4 months old: 10 ppm on grains and grain by-products; 30 ppm for distillers grains, brewers grains, and gluten feeds / meals derived from grains; total ration should not exceed 10 ppm and 50% of the diet
- For ruminating dairy cattle over 4 months old: 10 ppm on grains and grain by-products; 30 ppm for distillers grains, brewers grains, and gluten feeds / meals derived from grains; total ration not to exceed 5 ppm
- For chickens: 10 ppm on grains and grain by-products, not to exceed 50% of diet
- For swine: 5 ppm on grains and grain by-products, not to exceed 20% of diet
- All other animals: 5 ppm on grains and grain by-products, not to exceed 40% of their diet.