Harvest critical time for aflatoxin

Corn growers have consistently added yield over the past few years by taking advantage of continued improvements in corn hybrids. Adding consistently high quality and premium price to their corn crop in 2010 will be significantly impacted by how they manage aflatoxin.

Corn production in the Southeast is predicated on getting the right amount of moisture at the right time — too much or too little can affect growth, but it can also affect aflatoxin development.

Aflatoxin is a constant threat to Southeast corn growers — a threat they face at some level every growing season. If not managed, it can wreck a good corn yield by taking the profitability right out of the crop.

Ron Heiniger, Extension corn specialist at North Carolina State University’s Tidewater Agricultural Research and Extension Center in eastern North Carolina, says aflatoxin has been a topic of conversation for as long as he’s worked in the industry. “It seems like I’ve dealt with aflatoxin for my entire career, but I’d say it was about 1998-99 when it became clear to me the Southeast has a significant aflatoxin issue,” he said.

The North Carolina corn specialist points out, “Most of our North Carolina corn is grown for feed. However, we have a large demand for corn for human consumption in this area too. Because of aflatoxin concerns in our region, processors prefer to buy corn from the Midwest. It’s a deterrent to our local markets.

“There are direct implications where growers feel aflatoxin causes them to take a discount or make a crop insurance claim one year, but the wider impact of aflatoxin is that it negatively affects corn production in the Southeast, Heiniger said.”

At the grower level, Joe Etheridge, a grain farmer in Shawboro, N.C., says the price he gets from the premium market is critical to his bottom line. Sometimes Etheridge has to transport his corn more than 100 miles to sell, with profit margins so narrow and transportation costs so high, he says he can’t afford to have a load of corn rejected because of aflatoxin contamination.

Post El Nino years typically produce a higher than average number of hurricanes and less deadly tropical depressions. The combination of hot, dry weather, and intense and prolonged moisture and cloud cover and wind damage is an ideal scenario for aflatoxin to form, Heiniger said.

Most Southeast corn is going to be exposed to some type of stress prior to harvest, so afaltoxin and fumonsin fungi are likely to be present in damaged corn.

The first thing to do when considering what to do with damaged corn is to determine the type of damage. If the damage is primarily sprout damage, then it should be possible to harvest, dry, and store the grain.

However, sprout and other physical damage to corn is often associated with mold damage. Heiniger says, “If the corn is moldy, conduct a thorough and intensive scouting program for aflatoxin and/or fumonisin. Once the infection is established in the kernel, it flourishes in humid environments (85 percent to 95 percent relative humidity) and temperature from 75-90 degrees F.

In most years a combination of weather and chemical treatment can keep aflatoxin contamination low enough to meet Food and Drug Administration Standards of 20 parts per billion. However, the moist conditions associated with a hurricane and the condition of the crop will enhance the infection in the field.

As growers head into the critical growth period for corn in late June and into July, they may be wise to set the crop up as best they can for harvest. Harvest is a critical time for aflatoxin management — often times the difference in having a problem or not having a problem.

Having on-farm storage is usually considered an asset for marketing, but it can be the salvation for a corn crop that has been exposed to extended dry weather. If a grower can harvest corn early, quickly reduce the moisture level to around 12 percent, the chance of aflatoxin contamination is significantly reduced.

Harvesting and/or storing at higher moisture levels can be a double disaster in terms of aflatoxin. First, high moisture conditions favor growth of the fungus that causes the toxin to build up in corn. Second, damaged kernels provide a food source for the fungus.

Delaying harvest provides both time and an ideal environment for aflatoxin-causing fungi to grow, especially during periods of fluctuating moisture. The longer the corn sits in the field under these conditions, the more time the fungus has to produce aflatoxin.

Setting combines properly is another key to reducing post-harvest risk of aflatoxin contamination. University of Georgia researchers Dewey Lee and Paul Sumner suggest:

• Set fans at higher speeds to clean out light-weight, cracked grain and under-developed kernels.

• Slow header speeds to reduce initial kernel damage.

• Avoid picking ears that are in contact with the ground — these often have higher levels of aflatoxin

• Reduce combine cylinder/rotor speed to provide adequate threshing, but reduce seed coat damage.

• Install filler plates between cylinder bars to reduce physical damage to corn kernels.

In addition to good production practices, growers have some chemical weapons in their arsenal to protect corn against aflatoxin contamination. Bio-control, or naturally-occurring chemicals have worked in some cases.

A number of strobilurin-based fungicides can reduce the risk of aflatoxin development by slowing down transpiration and helping the corn plant cope with heat and drought conditions and use moisture more efficiently.

Etheridge says he had good results from treating some of his corn with Afla-Guard, a natural biocontrol agent which reduces aflatoxin levels in corn by producing a non-toxic strain of the Aspergillus flavus fungi that causes aflatoxins to form.

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