Example of poor tip fill and zipper ear from South Charleston, Ohio, this August.
By Peter Thomison, Corn Cropping Systems Extension Specialist
Drought and heat adversely affected ear and kernel formation in many Ohio corn fields this year. Poor ear and kernel development is associated with variability in plant growth within fields that is related to differences in soil moisture. In some areas within fields subject to protracted dry conditions, ears are absent (“barren”) or severely reduced in size with a few scattered kernels (nubbin ears). Where the impact of drought was less pronounced and plant height and color look normal or near normal, ear cob size may be normal but kernel number is markedly reduced. No kernels may be evident on the last two or more inches of the ear tip.
Several factors may cause this problem. The ovules at the tip of the ear are the last to be pollinated, and under stress conditions only a limited amount of pollen was available to germinate late emerging silks. Pollen shed was complete or nearly complete before the silks associated with the tip ovules emerge. As a result, no kernels formed at the ear tip. Uneven soil conditions and plant development within fields may have magnified this problem. Pollen feeding and silk clipping by corn rootworm beetles and Japanese beetles can also contribute to pollination problems resulting in poorly filled tips and ears.
Incomplete ear fill problems resulting from drought stress may also be related to kernel abortion. If plant nutrients (sugars and proteins) are limited during the early stages of kernel development, then kernels at the tip of the ear may abort. Kernels at the tip of the ear are the last to be pollinated and cannot compete as effectively for nutrients as kernels formed earlier.
Some agronomists and farmers characterize the kernel abortion that occurs at the end of the ear as “tip dieback,” “tip-back,” or “nosing back,” although poor pollination is also usually a factor affecting poor kernel set at the tip. Kernel abortion may be distinguished from poor pollination of tip kernels by color. Aborted kernels and ovules not fertilized will both appear dried up and shrunken; however, aborted kernels often have a slight yellowish color.
Zipper ears are another ear development problem evident in drought affected fields. Zipper ears exhibit missing kernel rows (often on the side of the cob away from the stalk that give sort of a zippering look on the ears). The zippering is due to kernels that are poorly developed and/or ovules that have aborted and/or not pollinated. Zippering often extends most of the cob’s length and is often associated with a curvature of the cob, to such an extent that zipper ears are also referred to as "banana ears".
For more information and pictures of these ear development problems and others ear abnormalities, check the following: “Troubleshooting Abnormal Corn Ears.”