Abnormal Corn Ears

Abnormalities in corn ears affect corn yield and quality. In most cases, abnormalities in corn ears originate from environmental conditions such as heat, drought, nutrient deficiencies, insects, and diseases, or through the misapplication of chemicals. Often, not much can be done to correct these issues, but proper diagnostics can prevent future issues.

Introduction to Abnormal Corn Ears

Over the last decade, several factors have been identified as being responsible for these ear abnormalities. The answer for each specific situation is yet to be determined. This document provides guidance regarding the potential causes for these issues and how to identify the abnormalities.

Potential factors affecting ear development

Some of the factors described by previous studies are:

Application of herbicides (some weeks before flowering),
Application of fungicides,
Environmental conditions around silking time (heat, drought, and nutrient deficiencies, among several other factors),
Insect damage in exposed ears,
Disease pressure, and
Hail damage, flooding, or other miscellaneous biotic or abiotic factors.

If the problem is associated with the weather, there is not much farmers can do to fix the problem. The environment influences ear development well before the silking period (R1 stage, flowering). In corn plants, the ear shoot is initiated by about V5 or V6 (five or six leaf stages), and final row and kernel numbers, two main critical components for corn yield, are ultimately determined when the potential number of kernels is finalized by around V15 (around 2 weeks before silking, depending on the environment, hybrid, and management practices).

Final ear size is a critical component in the determination of the final number of kernels in corn plants. These factors can be influenced by the environmental conditions from the V5 to V15 vegetative growth stages.

Arrested Ears

This symptom is associated with an unknown problem that occurs before the silking stage. Silk development is interrupted; thus ovules are not receptive for pollination and kernels do not form. The main causes related to this issue are unknown but can be associated with a condition that took place before flowering, around V10-V15. The response differs among hybrids.

Banana-shaped Ears

Banana-shaped ears develop when entire or partial kernel rows are aborted. The ears bend, taking the shape of a banana because of an uneven kernel number on the different sides of the ears. The causes are not clearly known, but could be associated with severe weather, herbicide misapplication, heat and drought stresses, and conditions before or at pollination.

Bouquet Ears

This condition Is characterized by the presence of several ears on the same node of the plant. The causes are not yet clearly identified, but can be related to heat stress during the early ear formation and development (V5-V15 growth stages), and pre-siliking misapplication of herbicides, fungicides, or insecticides.

A solution is to avoid misapplications of herbicides, fungicides, or insecticides during the late-vegetative period for corn (V10-VT). Some genotypes are more sensitive than others. A hypothesis previously suggested by Roger Elmore and Lori Abendroth (Iowa State University) is that the apical dominance of the main ear is lost, allowing the presence of multiple ears on the same node.

Disease Problems in Corn Ears

When ears are exposed from the husks, different disease problems can be evident. Some of the most common diseases are: diplodia ear rot, aspergillus ear and kernel rot, fusarium ear and kernel rot, gibberella ear rot, and blue-eye mold, among several other diseases.

Illustration 4 Examples of disease problems in corn ears. Disease problems in corn ears (pictures taken after silking stage) as the outcome of poor husk coverage.

Ear Stunting

Ear stunting is also referred to as "beer can ears" or "blunt ear syndrome." Ear size is abnormally limited, which offers a physical restriction for the final number of kernels, affecting primarily the total number of kernels per row. The occurrence of this abnormality may be related to the misapplication of chemicals, but the primary cause is still unknown. Ear size is defined before flowering, so any stress (biotic or abiotic) conditions affecting the crop during the mid- to late-vegetative stages could influence the size of the ear.

Exposed Ears

Exposed ears occur when the ear keeps elongating beyond the end of the husks. When this happens, the upper part of the ear is partially or completely exposed, which makes the ear more susceptible to any biotic or abiotic stresses (weather and pests in general). The cause of this, as suggested by Robert Nielsen, Purdue University, seems to be primarily related to the weather before or at pollination (heat and/or drought stresses) combined with a reprieve of those conditions after flowering. The combination of heat and drought early this season, followed by an unusually cool and wet pattern, has been the cause of exposed ears in Kansas.

Kernel Red Streak

Ears with kernel red streak have red pigment present in the kernels close to the tip section of the ear. This symptom appears when the wheat curl mite (Aceria tulipae) secretes "salivary phytotoxins" during the feeding process. This specific mite is a pest for wheat and carries wheat streak mosaic virus. As related to management practices, some corn genotypes tend to be more susceptible than others. In this particular case, the streaking does not affect the nutritional value of the corn. The discoloration can reduce the price obtained when the corn is sold for specific uses (e.g. food-grade corn).

Poor Kernel Set

Poor kernel set relates to lack of pollination, fertilization failures, or abortion after the ovules are fertilized, among other factors. The degree of severity ranges from just a few missing kernels to an ear showing mostly the cob with just a few kernels visible. Poor pollination or fertilization failure (due to pollen tube failure, desiccated and nonfunctional silks, no viable pollen) can be primarily related to warm temperatures and insufficient water supply during flowering. Other factors also can cause a similar pattern in corn ears, such as herbicides, nutrient deficiency (nitrogen and phosphorous), and insect feeding. Any biotic or abiotic factor that affects pollen shed or silk development and extrusion from the husks will interfere with the timing of pollen shed or silk development, which will cause fertilization problems and affect kernel set.

Poor Kernel Set / Herbicide-related Issues

Ears sometimes become malformed after misapplication of a herbicide, in this case glyphosate and AMS (ammonium sulfate).

Tassel Ears

Tassel ears occur when the tassel and the ear are present within the same structure. The tassel ears tend to appear at the top of the plant. The physiological explanation of this syndrome is not firmly known but seems to be related to the environment. This phenomenon seems to be more frequent in tillers, in plants close to the borders of the field, and under very low plant density levels with more isolated corn plants. The husks are absent, so the ear is not protected, and will be subjected to the influence of the weather, insects, and diseases.

Tip Dieback

Tip dieback symptoms become evident after pollination and are related to a failure in kernel set at the tip of the ear. The physiological explanation for these types of ears is related to poor pollination of fertile ovules, nonfertilized ovules where pollen is shed when silks were not yet extruded from the husks, and kernel abortion in the weeks after pollination until milk stage, R3. Any biotic (corn rootworm, Japanese beetles, foliar diseases, among several other factors) or abiotic (heat or drought stresses and nutrient deficiencies--specifically with nitrogen) stress can promote asynchrony between tasseling and flowering, which prevents undeveloped or late-developed ovules and silks from being pollinated. In addition, conditions before flowering can affect the kernels at the tip of the ear. These kernels are the most sensitive to stress conditions.

For More Information

Links for more information related to corn abnormal ears:

Credits

Author

Ignacio Ciampitti, Crop Production and Cropping Systems Specialist, Department of Agronomy, K-State Research and Extension

Photo Credits

Yanel Belich, Nidera S.A. Argentina

Ignacio Ciampitti, K-State Research and Extension

Stu Duncan, K-State Research and Extension

Doug Jardine, K-State Research and Extension

Tom Maxwell, K-State Research and Extension

Nathan Mueller, University of Nebraska

Kraig Roozeboom, K-State Research and Extension

Curtis Thompson, K-State Research and Extension

EP169 July 2014

K-State Research and Extension is an equal opportunity provider and employer. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended. Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, John D. Floros, Director.

Created By

Ignacio Ciampitti

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