Non-toxic fungus may hold key to aflatoxin contamination

Drought can deliver a double whammy to dryland corn farmers in parts of Texas.

First they get hammered by reduced yields. Then they face the very real possibility that harvestable corn may be contaminated with aflatoxin, which puts the kibosh on most market outlets.

A product developed by a USDA research plant pathologist in Arizona may offer hope, however.

Peter Cotty has isolated a strain of the aflatoxin-producing pathogen, Aspergillus flavus, that’s non-toxic and out-competes the toxic strain when applied on the soil surface. It’s already approved for use in cotton in Arizona and Texas and another strain is approved for peanuts in Georgia.

Farmers in two Northeast Texas counties tested the product in corn last year and say fields treated with the non-toxic fungus showed no signs of aflatoxin contamination.

Nearby corn fields showed aflatoxin levels from 14 parts per billion to 200 parts per billion. As little as 20 parts per billion may result in corn being rejected at elevators.

“Aflatoxin can be a problem especially in dryland corn,” says Grayson County, Texas, farmer Jack Norman, one of several Northeast Texas corn growers who used the experimental product, AF36, on a few fields last year under an Environmental Protection Agency permit.

“The problem occasionally shows up even in the Midwest,” Norman says, “but they usually have enough non-infected corn to blend to acceptable levels.”

“When we have problems we don’t have enough corn to blend,” says Bruce Wetzel, another Grayson County corn grower who used AF36 last year.

“Even in a good year, it’s hard to sell East Texas corn to poultry and dairy operations,” Norman says. That means most corn grown in this area is shipped to feedlots in West Texas. “We lose basis points. Freight costs to feedlots take away any market advantage we would have. We used to have a plus 50 cents per bushel basis. Now it’s minus 50 cents.”

“Egg producers may use some lower level aflatoxin corn,” Wetzel says, “but dairies will use none. It shows up in milk.”

“Just the threat of aflatoxin hurts our markets,” Norman says.

That’s why they’re excited about the potential for AF36.

“This is a strain of Aspergillus flavus that’s non-toxin producing,” Wetzel says. “Dr. Cotty developed it for cotton in Arizona and it has been labeled there on cotton for several years. Texas corn growers have been asking for a label for corn. The Texas Corn Producers Board is working to get a label.”

Wetzel says they introduce the non-toxic strain of Aspergillus in corn fields on sterile wheat seed treated with the fungus.

“The fungus colonizes the same areas on corn ears that the toxic strain colonizes. It gets a head start and if it’s already established the toxic strain is displaced.”

Cotty says timing is crucial. Last year most growers in the test area applied the sterile, treated wheat when corn was about waist high. “It was almost at canopy stage,” says Alton Norman, Jack’s brother.”

“We recommend applying the material just before the canopy closes to just before tasseling for best effect,” Cotty says. “We want to get more than a 90 percent reduction in aflatoxin levels. We will know more about the best timing when we get more experience with the commercial corn crop in this area.”

He said some farmers last year applied the material too late. “”Farmers in Grayson county timed it pretty good,” he says.

That canopy may be important, Wetzel says. “Sunlight might break it down.”

“About 10 pounds of sterilized wheat seed per acre is adequate,” says Jim Swart, Texas Extension integrated pest management specialist at Commerce. “That’s not much.”

Cost is relatively modest, about $6 per acre for the product. Currently, AF36 is distributed by the Arizona Cotton Research and Protection council, a non-profit organization made up of farmer members. Cotty says they provide the product at cost. Application techniques may need some tweaking, farmers say. “We have to sling it on,” Alton says. “We have some problems with aerial application near populated areas.”

“It’s sometimes hard to find (the treated wheat seed) after application,” Wetzel says. “But if we get moisture, we can pick up wheat seed and see fungus growing on it.”

“If it works, we’ll work out the logistics and figure out how to use it,” Jack says. “Last year I used a plane but only on selected fields away from populations.”

Last year was the first year Texas corn growers had an EPA permit to use AF36. Two counties in Northeast Texas and two in South Texas were selected for a two-year trial.

“We made a two-year commitment to plant continuous corn,” Wetzel says.

His son Chad says they hope the fungus will persist from season to season. “We hope to see some carryover. We’re not certain if the non-toxic fungus will become the dominant strain. We hope so. It worked great last year.”

Cotty says the fungus will overwinter so he expects some carryover effect. “We want all the farmers in an area to use it and reduce the level of the aflatoxin fungus.”

Jack Norman says results in 2008 were promising. “We had zero aflatoxin identified in the two fields we treated. Other fields ranged from 14 to 140 parts per billion. Surrounding farms recorded up to 200 parts per billion.”

Over the years farmers and researchers have speculated that insect damage could be a contributing factor to aflatoxin contamination but the Wetzel and Norman farms have identified aflatoxin on Bt corn.

“Drought and heat stress seem to be the key factors,” Chad says.

They’ll try the product again this year, in the same fields they treated in 2008.

“I’m not sure if we’ll use the same hybrids that we used last year,” Jack says. That could be a factor. “Some hybrids are more drought resistant than others. Late maturing, southern hybrids have more tolerance. The only other variety I had last year with zero aflatoxin was a long-maturing variety that was not treated with AF36.”

Wetzel says corn he planted last year in shallow soils was more stressed and showed more aflatoxin. “Also, if we harvest at higher moisture levels we’re less likely to have aflatoxin.” But that adds another cost to an already expensive production budget.

Jack says aflatoxin also affects cost of crop insurance. “With high risk we have higher premiums. We’re hoping we can get a break on insurance if this technology proves out.”

He also looks to increase insurable yield levels.

They hope to have approval for widespread use of the product soon. “It’s a naturally occurring fungus,” Wetzel says. “We’re just increasing the level.”

Cotty thinks EPA should approve the product but advises patience. “It’s already approved for cotton and we have done everything EPA asked. Farmers with contamination problems on cotton can already treat as many acres as they wish.”

He says several non-toxic strains of Aspergillus flavus exist and he believes different ones likely will work best in specific locations. “We have different climates across the Southwest. Conditions in Hidalgo County, for instance, are not the same as they are in Grayson County.”

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