By Joel DeRouchey, Josh Flohr, Jason Woodworth, Jordan Gebhardt and Katelyn Gaffield
Corn harvest in many locations across the upper U.S. has been delayed by rain and cooler weather that began in mid-September and now extends into early October at the time of writing this feature. This, along with some areas that experienced flooded fields resulting in higher than normal visibly damaged kernels, noticeable standing corn black mold/smoot prior to harvest, early reports of lower test weight from weather stress, and sprouted of kernels should be on the minds of nutritionists and production systems as they utilize corn in these identified areas.
Late-harvested corn resulting from prolonged early-fall moisture should be evaluated for various quality parameters. Some of these will include:
1. Damaged Kernels
While very little data is available to clearly assess the impact of the percentage of damaged kernels on swine performance, the type of damage may allow some predictions. Visually discolored, broken or cracked kernels, as well as sprout-damaged kernels, can indicate reduced nutritional value or the potential for mycotoxin contamination.
When damaged kernels are present, it is particularly important that the corn is dried to under 15% moisture. This will help prevent mold growth during storage, as damaged or broken kernels are more susceptible to storage related issues.
2. Mycotoxins
While many field molds grow in grains before harvest and require high relative humidity, there is also an opportunity for growth during prolonged cooler and wet conditions at harvest. Generally, the most concerning field molds are the Fusarium species, which produce vomitoxin, zearalenone and fumonisin. While quick tests can provide some guidance, it is difficult to determine the level of ‘harmful’ mycotoxins without a full chemical profile.
It is also important to remember that not all molds are harmful to swine/livestock. Often, black mold on corn ears may provide a visual warning of potential higher mycotoxin levels, but that is not always the case. Likewise, corn heat-stressed during the growing season, or corn with delayed harvest due to wet and cool weather, can show no signs of mold yet contain elevated levels of certain mycotoxins.
3. Low Test Weight
While 56 lb./bu. is the ‘normal’ test weight for corn, some reports in fall 2026 indicate corn in localized areas dipping to 50 lb. or lower. Most data evaluating lower test weights show that test weight must be 40 or below to impact feed conversion. However, most published data is over 25 years old and was completed in small pen settings. While still important to utilize, it is known as test weight decreases, less starch is present, resulting in less dietary energy. The practical challenge is a lack of published data with modern corn varieties to predict changes in feed conversion, if present.
