Wet Weather Raises Corn Quality Concerns

ISU Extension experts advising farmers how to deal with grain quality issues caused by recent heavy rains

Iowa State University Extension crop specialists are warning that the continued wet weather of the past couple of weeks has now reached the point where it has caused significant delays in harvesting and is causing potential damage to the 2007 Iowa corn crop.

As of October 14, 63% of the nearly 14 million acres of corn in the state remained mature yet unharvested. Little has been harvested since then.
Several ISU Extension crop and grain quality experts offer advice on how to handle the extreme moisture affecting the unharvested corn crop in Iowa. Here's how corn agronomist Roger Elmore, plant disease specialist Alison Robertson and grain quality specialist Charlie Hurburgh size up the current situation.

What is the current condition of Iowa's 2007 corn crop? The majority of the corn in Iowa that has yet to be harvested is still standing, yet some of it is lying on moisture-saturated soils. Therefore, it is vulnerable to all sorts of factors that could reduce yield, quality and profit. As delays in harvesting continue, farmers can expect to experience plant and grain quality issues. Extended rain periods expose crops to saturated soil conditions, ponding and continual wetting of plant tissue. There are two areas of concern for the corn crop remaining in the field: stalk quality and standability---and grain quality.

Stalk quality and standability are concerns.

About 18% of Iowa's unharvested corn is either moderately or heavily lodged, according to the USDA weekly crop conditions survey report released last week.

"It's a discouraging problem at harvest time when you have fields or areas of fields that are lodged," notes Elmore. "Lodged corn not only slows down harvest dramatically, but it also increases the possibility of harvest losses. Corn that is in flooded areas of fields will not likely keep standing for much longer, which will predispose the ears to an increased chance of mold infections."

Ears on some hybrids stay upright and/or have open husks. Upright ears and open husks can serve as funnels and receptacles for water. Given enough moisture and warm temperatures, corn on the ear will germinate and thus reduce grain quality.

With the persistent damp weather this fall, many farmers have noticed a change in the color of corn plants in the fields. They describe these plants as being covered with a blackish soot. A sample brought into the ISU Plant and Insect Diagnostic Clinic contained this black growth, says Robertson. This growth was primarily due to a fungus called Alternaria, although there were likely other fungi present (including Colletotrichum).

Alternaria is a common decay fungus, which decomposes dead organic matter, she explains. Although Colletotrichum is often a pathogen earlier in the growing season, it is also a common saprophyte, an organism that feeds on decaying dead organic material late in the season. This discoloration of plant tissue will not affect grain yield or quality yet it will likely increase stalk degradation, she says.

Ear rot and mycotoxin contamination risk.

High moisture conditions favor growth of many ear and stalk rot fungi, increasing the risk of ear rots and mycotoxin contamination.

Fields should be scouted as soon as possible to determine the extent of disease problems, says Hurburgh. To minimize losses due to ear rot and increased mycotoxin levels, it is recommended that farmers harvest problem fields as soon as possible. The longer the corn remains in the field, the greater the chance of toxin production.

The toxins of most concern to increase in the field at this time are the fusarium-based toxins, vomitoxin and fumonisin. He advises farmers to adjust their harvest equipment to minimize damage to kernels since mold and mycotoxin levels tend to be at greater levels in damaged kernels. "You should dry the grain to less than 15% moisture and cool it to less than 45 degrees F as quickly as possible to reduce further mold growth and toxin production," says Hurburgh.

Elevators see higher levels of mold in corn.

Elevator operators are reporting cases of mold damage levels 5% and higher in the current corn crop, with an unusual mix of mold types, and sprouting from prolonged moist conditions. In normal years, overall mold damage levels are generally less than 2% in freshly harvested corn.

High damage levels in harvested grain create challenges for grain grading, particularly in the harvest rush. Damaged corn sharply reduces the future storage life of the grain. Corn that had black layered, even if it was at high moisture, was past experiencing economic injury from frost. However, corn that was green will likely have lower test weights, which is another source of reduced storage life.

Storage and harvest management will be particularly important. "Field damaged grain, regardless of reason, should not be mixed with good grain," emphasizes Hurburgh. "Farmers should harvest around water holes, downed grain and frost damaged areas. Do not mix your damaged grain with your good grain in storage either. The damaged or low test weight grain must be aerated immediately to reduce temperature and equalize moisture."

Damaged grain has shorter storage life.

Field damaged grain will not store beyond the winter months, says Hurburgh. He says with field damaged grain, you should maintain 1 to 2 percentage points lower moisture than normal grain. For example, you'll want to dry this corn down to 13% moisture content instead of the more typical 15% moisture.

If you suspect mycotoxin problems, check with your crop insurance provider to see if adjustments may be needed, and how to represent the areas to be adjusted. Crop adjustments for quality problems, including mycotoxins, must be done on standing corn at or before harvest.

Accurate grading of field-damaged grain is always difficult in the rush of harvest. Expect end users, such as ethanol plants, to increase their level of grading because mold and weather damage reduce processing yields and the quality of the distillers grain byproduct. An official USDA grade is the standard against which buyer analysis should be compared.

Hurburgh says it is important that company graders be trained to match USDA graders. Alternatively, grain samples can be submitted to USDA grading agencies but this process is slower and more costly. In the event of a dispute, you should use an official USDA grader. The variety of damage types will be very challenging to evaluate. See http://www.gipsa.usda.gov/GIPSA/webapp?area=home&subject=fc&topic=fsp to locate the official agency in your area.

Take steps to improve grain storage quality.

Precleaning grain prior to storage is generally a good practice but can be critical for badly damaged corn, says Hurburgh. Pre-germinated corn can typically be removed using most screening operations. Kernels with extensive mold damage can frequently be removed with simple air separations but this may not be sufficient to reduce mycotoxin levels to safe levels.

Separation equipment is available for removal of additional infected kernels but the additional operations required are rarely economically viable for commodity corn. In these situations, you should level the grain in the bins after filling, provide adequate aeration to reduce moisture migration, and monitor temperatures for "hot spots" to help control growth of fungal storage pathogens.

Corn that has not dried early in the harvest period often stops at 17 to 18% moisture content in the field. It is very important to cool this corn immediately and dry it as rapidly as possible, says Hurburgh. Natural air drying systems will have difficulty if the humidity levels remain high. Check stored corn frequently and consider delivering to market if problems start to appear.

Watch grain quality for livestock feed.

Robertson points out that livestock (swine, cattle, horses, poultry) are susceptible to certain mycotoxins. Thus, any grain that is fed to livestock should be tested for mycotoxins. Dairy producers should be particularly sensitive to mycotoxins.

The wide variety of molds on these grain samples has created a range of mycotoxin possibilities – aflatoxin, vomitoxin, fumonisin primarily. Most recently fumonisin has been found in a number of high-rainfall areas. The prolonged cloudy, humid weather encourages production of the fusarium-based toxins.

Veterinarians can submit samples to the ISU Veterinary Diagnostic Lab at Ames. Alternatively, Official USDA grading agencies can do quick tests for these toxins. Toxins concentrate in the distillers grains to three to four times the levels they do in the corn grain. That's why ethanol plants are doing quick screening tests on inbound grain, especially on low test weight corn—corn that is less than 50 pounds per bushel.

For more information, the ISU specialists recommend you see ISU Extension publications PM 1800, Aflatoxins in Corn, and PM 1698, Corn Ear Rots, Storage Molds, Mycotoxins, and Animal Health for guidelines on sampling and sample handling. The black light test responds to only aspergillus that produces aflatoxin and will not detect fusarium, says Robertson.

Food grade corn requires special caution.

Current conditions are a serious concern for edible products such as popcorn or white corn intended for human consumption, notes Elmore. These are typically higher value crops with limited product volume so additional separation steps to remove contaminated kernels are a fairly common practice.

How difficult is it to separate contaminated grain from good grain? Fungal toxins are frequently concentrated in a few highly contaminated kernels, explains Hurburgh. Individual kernel levels of aflatoxin have been reported up to about 8,000 ppb. Removal of the infected seeds to reduce mycotoxin levels prior to milling is a fairly common practice.

Limited research has also been done on corn separation methods but industrial applications of these methods are less common due to typical lower mycotoxin levels and the commodity nature of corn. A portion of infected kernels can frequently be removed using more advanced cleaning devices to remove low density and/or discolored kernels. Hurburgh says both methods have been fairly effective at reducing mycotoxin levels by removing kernels with different physical or optical properties.

ISU Extension publications PM1800, Aflatoxins in Corn, and PM 1698, Corn Ear Rots, Storage Molds, Mycotoxins, and Animal Health can be ordered through any ISU Extension county office, online at http://www.extension.iastate.edu/store/ or by calling the ISU Extension Distribution Center at (515) 294-5247.

TAGS: USDA Extension
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