April 14, 2010
AMES, Iowa — New research on hail-damaged corn led by Iowa State University shows that hail damage during grain fill increases the risk of ear rot diseases and mycotoxin contamination.
The findings are important because hail-damaged corn is often used to feed livestock, which can become ill or refuse feed if mycotoxin concentrations are too high.
"Hail damages crops somewhere in Iowa every year. But until recently, there was little data to quantify effects of hail damage on grain quality," said ISU plant pathologist Alison Robertson.
Robertson studied the issue with ISU colleagues Charles Hurburgh, director of the Iowa Grain Quality Initiative; Gary Munkvold, Seed Science Endowed Chair and plant pathologist; and Steve Ensley, clinician with the Veterinary Diagnostic Laboratory.
Robertson analyzed injured corn ears collected from several Iowa fields damaged in two major hail storms in July and August 2009. The storms affected 1.3 million acres in northeast and west-central Iowa. Because they occurred in later stages of the crop's growth, these storms offered a rare chance to study effects of hail on grain quality.
One way grain quality declines is through growth of molds on hail-bruised kernels. Some molds produce toxins leading to ear rots; others discolor kernels, reducing marketability. The researchers wanted to answer a common grower question: What impact does hail damage to developing kernels have on corn grain quality, ear rot severity and mycotoxin contamination?
They found that as hail damage to kernels increased, so did severity of ear rots — and with the ear rots, the presence of certain mycotoxins.
Fusarium, Gibberella and Cladosporium were the main molds found in the study. Fusarium ear rot can contaminate grain with toxins called fumonisins. The toxins deoxynivalenol and zearalenone are produced by the fungus that causes Gibberella ear rot.
Cladosporium does not produce toxin but does create black mottling on kernels, Hurburgh said. "This classifies as "˜total damage' in the official U.S. grades and therefore creates marketing issues."
Researchers also found that where deoxynivalenol — more commonly known as vomitoxin — was found, zearalenone was usually present as well.
"Swine are very sensitive to vomitoxin," Robertson said. "And zearalenone is an estrogen-type mycotoxin that can affect breeding pigs."
Because zearalenone poisoning affects reproduction, effects are hard to see. But vomitoxin, to which swine are most sensitive, causes more visible signs of sickness such as poor weight gain, Ensley said.
The mycotoxins may enter livestock feed through feeding corn or dried distillers grains (DDGs), which are a by-product of the ethanol-making process. When damaged grain is used to make ethanol, any mycotoxins present concentrate up to three times in the resulting DDGs, Robertson said.
To counteract this, contaminated grain or DDGs may be blended with clean grain to get below FDA advisory levels. For swine, the FDA advisory limit for vomitoxin is 5 parts per million, or not more than 1 part per million of total diet, and 1 part per million for zearalenone. The researchers did not blend grain for this study; but they found about 10 percent of pure grain samples had mycotoxin levels above the FDA advisory limits for vomitoxin, zearalenone or both.
"This amount may seem small, but you need to factor in that approximately 65 percent of Iowa's corn is used in the ethanol industry," Robertson said.
Because of this, and mycotoxin concentration in DDGs, Robertson said that "in actuality, more than 50 percent of the study's grain samples had mycotoxin levels that would have concentrated in the DDGs to levels greater than FDA advisory levels."
Even when blending grain, it can be hard to get an even distribution of clean and contaminated grain in the feed mix, Ensley said.
"It's hard to get a homogenous mixture. There could be areas in the feed where concentrations of contaminated grain are higher," he said. "Pigs are so sensitive to DON, this may cause them to go off feed and it may take two weeks to get them consuming feed normally again, even on totally clean grain."
Robertson said the results illustrate the importance of regularly checking fields to monitor development of ear rots, and making plans to harvest as soon as possible if more than 10 percent of ears in a field are considerably moldy.
The good news, she said, is that pre-harvest scouting of fields is an effective way to cut risks of mycotoxin contamination.
"Our research showed there was a positive correlation between visually damaged samples and detectable levels of toxins," she said. "So, it's very important to scout your fields to see how much ear rot you have.
"Our management recommendation is to harvest this damaged grain as early as possible, and dry and cool the grain immediately to reduce growth of molds and minimize further development of these mycotoxins."
The research was funded by the ISU College of Agriculture and Life Sciences, ISU's Iowa Grain Quality Initiative and the ISU Corn and Soybean Initiative. ISU Extension field agronomists and Corn and Soybean Initiative partners collected the samples used in the study. It is currently being prepared for publication in a peer-reviewed journal.