by Gretchen A. Mosher
Iowa rainfall in 2026 has arrived in “big buckets,” with above-average temperatures and rainfall raising concerns about crop quality and post-harvest storage.
Almost three-quarters of Iowa’s weather stations reported at least 4 inches of rainfall or more in September, according to Iowa State University’s Mesonet data. As fields begin to dry out, several concerns have emerged about grain quality, both in the field and after harvest.
Corn concerns
A key concern for corn is the growth of fungus and field mold, especially ear rot. Ear rot decreases yield and reduces the food, feed and grain quality of harvested grain. Some fungi that produce ear rot also may produce mycotoxins, which are hazardous to animals and humans. Mycotoxin-contaminated grain must be segregated from noncontaminated grain. It should not be blended with “clean grain.”
Much of the harvested corn will have higher-than-normal moisture content. Higher temperatures would increase crop quality pressure, but even at lower temperatures, corn will retain its high moisture levels.
Where in-field mold is present, some yield loss should be expected, along with decreased storage life. Read more on ear rot from the Crop Protection Network.
Increased precipitation has flooded crop fields across the state. Crops flooded by water from rivers, streams or irrigation canals are considered adulterated. Legally, the term adulterated means that the grain cannot enter commerce as either human or animal food and must be destroyed.
For more information on managing flooded grain, check out the following resources:
- “Management guidance for flooded grain”
- “Proper disposal of flood-damaged grain”
- “Guidance for evaluating safety of flood-affected food crops”
Soybean quality concerns
As with corn, quality concerns with soybeans exist this fall as the result of recent wet weather that will impact harvest and storage.
Purple seed stain in soybeans is caused by the Cercospora kitkuchii fungus, which expresses on the seed coat of the soybean. While the disease does not usually impact yields, it does influence grain quality.
To limit the impact of contaminated soybeans, control moisture levels post-harvest.
To address purple soybeans, try these post-harvest strategies:
Prioritize a timely harvest. Leaving infected soybeans in the field with warm, wet fall weather will increase the likelihood of secondary molds and rapid seed decay, accelerating structural damage of the beans.
Cool and dry soybeans quickly. Dry soybeans to 13% moisture content to mitigate continued fungal metabolic activity. Cool grain bin temperatures to 35 to 40 degrees F as soon as outdoor temperatures cool. Cercospora grows well between 75 and 80 degrees F, so cooling the bin temperature is important.
Consider screening and cleaning operations. Run harvested soybeans through pre-storage screeners. Cleaners cannot lift the purple stain out of stained seed coats, but they remove foreign material, split beans, and eliminate pockets of moisture and foreign material that may protect molds and fungi.
Other soybean quality-related effects include bean pod splitting and seed sprouting. Splitting is one result of swollen beans that have excess moisture, exposing them to additional moisture from rain.
Compromised or sprouting soybeans are more susceptible to fungal growth. Split or sprouting soybeans also may release free sugars and fatty acids, leading to rapid spoilage in storage.
Damaged soybeans tend to have lower test weight or damaged seed coats, both of which will result in price dockages at the time of sale. Shrunken or sprouted seeds also may get caught in the combine. Read more on adjusting combine settings for changes in crop quality.
When storing soybeans, the target moisture content is 13% or lower, and 11% to 12% for long-term storage. Soybeans that have a moisture content greater than 13% to 15% must be dried to prevent rapid mold growth, heating or quality loss.
Grain elevators vary in their management and willingness to accept high-moisture soybeans. Some will not accept soybeans at moisture higher than 15%, while others may be willing to accept wetter beans but will take a discount.
How to handle wet crops
Here are eight tips for handling and storing wet corn and soybeans:
1. Watch for fungus development. Wet and warm weather encourages the growth of fungus on corn ears and ear rot. Some of these fungi produce mycotoxins that are harmful to animals and humans.
Deoxynivalenol or vomitoxin is associated with Gibberella ear rot, grows in cool and wet conditions, and may be present this fall. Screening for toxins by feed mills and ethanol plants should be expected, especially if fungus emerges on ears.
2. Monitor fields before harvest. Pre-harvest field scouting can help identify fungal and potential toxin incidence. Approach harvest with an eye on efficiency.
Once harvested, dry corn down to 15% or lower moisture as rapidly as feasible. This will not remove existing toxins and mold, but it may prevent further growth.
3. Pay attention to shelf life. Moldy grain has a shorter storage life than clean and dry grain held at the same temperature and moisture — generally between 60% and 70% of its normal storage life. Avoid holding wet grain for extended time before drying, as this will decrease the storage life further.
4. Utilize monitoring tools with stored grain. Once grain is in storage, the ongoing monitoring of temperature and carbon dioxide is key to prevent large-scale quality issues. Deteriorating organic matter produces carbon dioxide and, along with temperature monitoring, is one of the best ways to identify mold, hot spots and spoilage in stored grain.
5. Consider a composite sample. Commercial elevators, feed mills and ethanol plants should consider implementing the practice of taking a composite sample for each half-day of samples containing all loads received during that half-day timeframe. Composite samples help to monitor, segregate and contain toxin contamination.
6. Take care in checking stored grain. There will be out-of-condition grain in 2026. Grain that is out of condition is the primary cause of grain engulfment and entrapment.
Take extreme care when checking and handling high volumes of wet corn and soybeans. Especially during the rush of harvest season, use safe practices when working with machinery and in loading and unloading harvested crop.
7. Dry soybeans carefully. Soybeans are more fragile than corn, and they may crack or split more easily than corn, especially under high-temperature mechanical drying. For continuous-flow dryers, keep the drying temperature below 130 degrees F, and for batch dryers, keep it below 100 degrees F.
8. Keep an eye on relative humidity. To minimize damage to the seed coat and to prevent splits, maintain a relative humidity at 40% or higher. Keeping relative humidity high can be challenging when air is heated, so be mindful of both temperature and relative humidity.
Mosher is a professor in the Iowa State University Department of Agricultural and Biosystems Engineering.