Whole cobs with some attached kernels behind the combine are a clue that a narrower concave spacing or a faster thresher speed may improve shelling. If a few soft, immature cobs break up without removing all the kernels, don't be concerned. A fast thresher speed breaks cobs excessively and increases kernel damage. If too many wet cobs shell poorly, don't thresh too aggressively. Delaying harvest to allow more field drying may solve this.
Cobs splitting down their length is usually due to a narrow concave gap.
Corn Quality Within the typical harvest moisture range, threshing is the likely cause for cracked kernels. Concave gaps narrower than e inch or thresher surface speeds above 3500 feet per minute can lower corn below USDA Grade No. 2 requirements. If adequate aeration is available in storage, corn kernel damage essentially determines the maximum allowable storage time. About 90 percent of the separation should occur at the thresher. Gentle threshing aids corn recovery on the walkers and sieve.