With the “Bar Bell” deformity, kernel formation is normal at the base and tip of the ear but absent from the middle of the ear.
This problem is associated with chilling injury during ear formation and more evident in certain sweet corn genetic backgrounds. Low temperatures disrupt normal kernel development resulting in anomalous ear growth.
Avoid planting hybrids susceptible to this abnormality especially under conditions where cold temperatures during ear formation is likely.
Lipps, P. 2008. Personal Communication. Ohio State University.