Farm Talk


May 21, 2014

Aflatoxin risk looms large for corn growers

Parsons, Kansas — To diversify their farms and tap into high demand for one of agriculture’s most profitable crops, dryland farmers more familiar with growing wheat and milo are eager to try their hand at corn.

But despite a push by seed companies to develop drought tolerant varieties that require less water, planting non-irrigated corn is still a gamble.

One of the most significant obstacles is the potential for contamination from aflatoxin, a naturally occurring toxin produced by certain kinds of fungi. The thick gray-green mold that appears on corn ears is primarily brought on by heat and drought stress, which means in recent years it has had ideal conditions for flourishing in dryland fields.

In 2012, the drought was so widespread that aflatoxin even appeared in parts of the Midwest, leading to the largest outbreak on a national scale since the 1980s. On several occasions, the Food and Drug Administration has waived its “no-blending” policy for aflatoxin-contaminated corn in Kansas and Oklahoma to deal with the problem. According to crop insurance data from the U.S. Department of Agriculture, payouts for mycotoxins — of which aflatoxin is the most common — have reached as high as $75 million in a single year.

Grain industry officials, farmers and end users from Oklahoma and the surrounding region had an opportunity to hear recently from several experts about strategies for testing, storage, management and prevention of infection.

Peter Cotty, a research plant pathologist and lead scientist for the Ag Research Service based at the University of Arizona at Tucson, told the audience the toxic chemicals produced by the Aspergillus fungus are considered a human carcinogen.

“It’s very toxic, more toxic than the most toxic pesticide that’s currently listed for use,” added John Damicone, a plant pathologist at Oklahoma State University.

As a result, tolerance levels are strictly regulated. Limits are set at 20 parts per million for corn sold into domestic or export markets. That’s also the upper limit for corn fed to lactating dairy cows (milk cannot exceed .5 ppm) and for younger classes of hogs and poultry and as well as beef cows used for breeding purposes. Ethanol plants typically won’t accept contaminated corn because the toxin becomes concentrated in distillers grain products sold for feed.

The most common way of managing it is for elevators to blend it off, a process done under state and federal oversight, but the challenges associated with handling tainted grain can prompt steep discounts and even load rejections.

Farmers in Texas are all too aware of the losses that can result, and two of them shared their experiences at the informational meeting, which was held in Enid, Okla.

Back in 2005, former county agent and corn farmer David Gibson, of Tulia, Tex., sold infected corn for 25 cents a bushel and waited two years to settle the resulting insurance claims.

Sometimes infestation levels are so high, the crop can’t be salvaged at all. That’s what happened to Scott Averhoff, who farms at Waxahachie south of Dallas. After he was forced to destroy 900 acres several years ago, he joked that his wife strongly urged him to run for the Texas Corn Producers Board so he could learn more about the problem and how to prevent it. Now he’s in the business of distributing a biological control agent, a topic much discussed during the meeting.

Prevention is the best medicine. Experts recommend producers reduce plant stress with proper fertilization and by planting early to avoid high nighttime temps. Crop rotation is also beneficial.

But the experts who spoke in Oklahoma also touted biological control as one of the best pre-emptive steps available.

“When I started out, I was a skeptic about biological control,” Damicone said. “But I learned from doing my master’s research, it’s the only thing that actually works.”

Biological control involves spraying a field with a different strain of the same fungus that doesn’t produce the toxin, in hopes of crowding out the toxin-causing strains. Cotty credited it with being 80 to 85 percent effective.

“You get some hold-over from year to year, so the benefits build up over time,” added Cotty, who is considered a leading expert on aflatoxin control around the world. “If everyone does it, it can work like a regional control plan.”

Better bin management

Managing the problem extends beyond harvest. Carol Jones, an OSU ag engineering professor and research engineer, talked about how storage affects mold growth and spread.

Many commercial grain bins in Oklahoma lack the aeration systems common further north that prevent condensation caused by big temperature swings and high relative humidity, she noted.

Growth of Aspergillus fungus, which causes aflatoxin, is optimal at temperatures between 80 and 100 degrees with a relative humidity around 85 percent (corresponding to 18 percent grain moisture.) Conversely, fungal growth is minimal below 55 degrees, so grain needs to be kept cool and dry, she said.

Cleaning equipment and bins, avoiding kernel damage during handling, installing proper ventilation and using bin spreaders can all improve the quality of stored grain and prevent further contamination, Jones explained.

Brent Kisling, executive director of the Enid Regional Development Alliance, which hosted the meeting as a follow-up to an ARS-USDA listening session in January, said the turnout of around 60 grain officials indicated they are eager to work with farmers to expand and diversify cropping options.

Even so, the weather continues to pose challenges. Most of the southwestern third of the country is in the grip of another severe dry spell. Through August, the National Climate Prediction Center is calling for drought to persist or intensify across Southern Kansas, Southwest Missouri and much of Oklahoma and Texas.

“So far 2011 was the worst drought we’ve had,” said Gibson, the Texas panhandle farmer. “But I’m not sure 2013 isn’t going to be worse.”


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