RL (Bob) Nielsen, Agronomy Department
Once ovules on ears of corn have been successfully fertilized by pollen captured by the silks, the kernels that subsequently develop may abort if severe photosynthetic stresses occur during the first 2 to 4 weeks after pollination. The most typical position or pattern of abortion is that of the kernels near the tip of the ears because they are usually the last to be fertilized by pollen and, thus, are younger and more vulnerable to stress than the older kernels below them on the cob. However, sometimes kernels abort down one entire side of a developing ear, resulting in what is commonly referred to as “zipper” ears. The pattern consists of 1 or more rows of aborted kernels. No one knows for certain why this “zipper” pattern of kernel abortion develops, but we do know it is not restricted to any specific stress, but rather to severe photosynthetic stress of any kind. The ears in the accompanying photos were taken from a nitrogen (N) rate trial in plots that received only 30 lbs of N. In these plots, leaf death or “firing” was visible as high as 1 or 2 leaves below the ear leaf by the early dent stage of kernel development when the ears were taken. Similar “zipper” kernel abortion patterns can occur in response to severe drought stress, severe foliar disease, or severe defoliation by hail that occurs or exists during the first few weeks of kernel development following pollination.