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Wet weather raises corn quality concerns

Agriculture.com Staff 10/23/2007 @ 7:06am

Rain has caused significant delays and potential damage to the Iowa corn crop.

As of last week, 63% of the nearly 14 million acres of corn in the state remained mature yet unharvested. Little has been harvested since then, according to an Iowa State University (ISU) Extension report.

Several ISU Extension crop and grain quality experts offer advice on how to handle the extreme moisture affecting the unharvested corn crop in Iowa.

The majority of corn is standing, yet some is lying on moisture-saturated soils, and, therefore, is vulnerable to all sorts of factors that could reduce yield, quality and profit. As delays continue producers 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.

Eighteen percent of Iowa's unharvested corn is either moderately or heavily lodged, according to the USDA National Agriculture Statistics Service report released earlier this week. There are few more discouraging harvest problems at this time of year than to have fields or areas of fields that are lodged. Lodged corn not only slows down harvest dramatically, but it also increases the possibility of harvest losses. Flooded corn will not likely stand 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 reducing grain quality.

With the persistent damp weather, many have noticed a change in the color of plant tissue described as blackish soot. A sample brought into the ISU Plant and Insect Diagnostic Clinic contained this black growth. 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.

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.

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. To minimize losses due to ear rot and increased mycotoxin levels, it is recommended that producers 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 fuarium-based toxins, vomitoxin and fumonisin.

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