Don’t panic – but be on the lookout for corn with potential Aspergillus-ear-rot-caused mycotoxins. That warning is from Purdue University plant pathologists advising you to scout fields for ear rot that could lead to grain toxic to livestock and humans.
They’re cautious because of the late-season drought stress in some fields and the potential for further problems this fall.
“Because of the weather, I’ve been getting a lot of calls about the potential risk of aflatoxin problems caused by Aspergillus ear rot (AER),” says Charles Woloshuk, Purdue Extension plant pathologist and co-author of Diseases of Corn: Aspergillus Ear Rot.
Woloshuk surveyed many fields in late summer looking for ear-rot diseases. “In mid-August, it’s impossible for anyone to predict whether we will have widespread problems,” he says. “But I have learned over the years that fall has a great impact on how things will go. If we get a fast drydown of the corn this fall, this will slow the mold growth. If we get big rains from tropical storms things might be worse.”
Woloshuk says parts of Indiana and the eastern Corn Belt have sandy or very light soils, which are more “likely to be affected by drought and heat stress, and they may have issues with aflatoxin. People need to scout fields. Start in fields where plants look stunted and stressed, in light soils and hillsides.”
University of Illinois (U of I) plant pathologists say AER symptoms include patches of green to yellow spores on or between kernels. It is most common at ear tips and scattered on a few kernels on ear. The fungus can become dark green to brown as it ages.
U of I says Aspergillus flavus and other Aspergillus can also cause storage rot. In favorable conditions, Aspergillus can invade kernels with moisture levels as low as 14%. Kernels are more likely to be invaded by fungi if they have come from rotted ears or if they’ve been damaged.
Woloshuk says growers should scout for AER by collecting multiple ears from several locations and checking them for olive-green mold.
“If areas of the field have rot, farmers should avoid them during harvest,” he says. “Fields with extensive disease should be harvested as early as possible and dried to moisture levels that stop fungus growth.”
Richard Stroshine, a Purdue ag engineer, says it’s difficult to rid a field of AER. “The spores are always there, and it will grow if conditions are right,” he says.
“You may be able to reduce the levels by sifting out the fines, where we often see higher levels of toxins. Consider a screen cleaner that has a larger opening so that only the small kernels and fines fall through.”
Stroshine says that in 2009, “we saw a lot of Gibberella ear rot,” which can cause vomitoxin. “I worked with one farmer who used a rotary screen cleaner to remove smaller kernels. However, it reduced toxin levels for one hybrid but not another,” he says.
No commercial corn hybrids are resistant to AER, but Woloshuk says farmers can take some steps to help minimize its growth. "Hybrids that tolerate water stress and irrigation can reduce drought stress on the plant,” he says. “Also, growers should maintain appropriate field fertility.”
With concerns about molds and mycotoxins across much of the Corn Belt in recent years, it’s important for storage and handling facilities to avoid potential carryover contamination. Here are some storage tips from Richard Stroshine, Purdue ag engineer:
• Thoroughly clean grain dryers, bins, trucks and other grain-handling equipment before harvest.
• Uniformly dry corn to a safe storage moisture. If mycotoxins are a concern, storage moisture should be 0.5-1% lower than normal.
• Remove fine material, which caninterfere with drying and aeration and often contain higher toxin levels.
• Cool stored grain as outside temperatures drop. Fungal activity is greatly reduced between 35° and 40°F.
Stroshine urges growers to wear a respirator capable of filtering fine dust particles. “Even a little spoiled grain can produce millions of spores that can irritate lungs and cause severe reactions requiring hospitalization,” he says.