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Abnormal Ears in Corn—When and Why Do They Develop?

ANR-0139
Agriculture and Natural Resources
Date: 
07/24/2023
Osler Ortez, Assistant Professor, Corn and Emerging Crops, Department of Horticulture and Crop Science, The Ohio State University

After more than 100 years of studying corn, questions still exist about its growth and development. Corn ear abnormalities have been reported for over a century. To date, ear development issues reported in cornfields persist, reducing productivity and spurring research about the underlying causes.

Distinct differences exist between normal and abnormal ears, one being their yield capacity. Abnormal ears show distinctive disruptions in cob, kernel, or husk leaf development. Abnormal ears can include:

  • tassel ears
  • arrested ears
  • ears with cob curvatures
  • ears without viable or exposed silks
  • ears with unusual patterns of failed pollination or kernel abortion
  • plants with more than one ear on the same ear shank
  • ears with kernel skips along the cob
  • ears inadequately covered by husk leaves

In 2016, widespread ear abnormalities were reported in the western and central U.S. Corn Belt (Kansas, Nebraska, Iowa, and Illinois), Eastern Colorado, and the Texas Panhandle. A survey in 15 Nebraska grower fields provided important results:

  1. Affected fields averaged 26% of abnormal ears, with abnormal ear production ranging between 12 and 49% (that is 12 to 49% of plants had abnormal ears).
  2. Abnormal ears reduced grain yield 35–91% (yield loss per area depends on the symptom, its frequency, and its severity).
  3. The placement of abnormal ears suggested that abortion of the primary ear was a correlated factor (Ortez et al., 2022a). In addition to lower yields, reduced grain quality could also be expected.

Recent research confirmed that ear abnormalities are the result of cumulative interactions among genetics (e.g., hybrid-specific, variable hybrid responses), environment (e.g., stress factors), and management practices (Ortez et al., 2023). For example, crop stress conditions driven by unfavorable growing conditions (environment), susceptible hybrids (genetics), high or low seeding rates (management), and their interactions affected ear abnormality results in this eight-site, yearlong trial. These interactions led to lower or higher numbers of ear abnormalities, affecting the severity and frequency of these issues, impacting the degree of yield losses.

Corn Growth and Development

The crop’s exposure to unfavorable conditions during the growing season can negatively impact ear formation and yield (Diagram 1). Understanding the conditions that may affect corn ear formation, yield, and result in abnormal ears is critical. Understanding the underlying factors responsible for abnormal ears must include identifying when the potential stress occurs relative to yield formation. Corn grain yield includes three main components. These components are determined at different times during the growing season:

  1. ear number per unit of area (early in the season)
  2. kernel number per ear (mid-season)
  3. kernel weight (late in the season)
Diagram displaying the initiation and growth period for corn crops, extending from germination to maturity.
Diagram 1 (click diagram to view enlarged image). Initiation and growth period for aboveground plant structures extending from germination (G) to physiological maturity (R6). According to literature reports, the horizontal brown arrows indicate the main period when the event occurs, and the thin horizontal gray arrows indicate possible time variations for each event. The ear shoot initiation arrow refers to the initiation of primary ear shoots. Kernel primordium initiation refers to the initiation of florets, which may form kernels if properly developed, pollinated, and fertilized. Diagram originally adapted from Abendroth et al. (2011), McMaster et al. (2005), and McMechan et al. (2017). Source: Ortez et al., 2022b


Based on existing knowledge, a literature review summarized abnormal ears’ symptoms, identified possible causal factors, and postulated development timing (i.e., when the stress may have occurred). Thirteen symptoms of corn ears were reported, including tassel, fasciated, arrested, pinched, blunt, silk-balled, incomplete kernel set, banana-shaped, zipper, tipped-back, multi-ears, barbell-ears, and short-husk ears.

Abnormal Ear Symptoms, Factors, and Development Timing

Based on existing knowledge, the following gallery figures (1 through 13) and Table 1 present a summary of abnormalities, including the possible causal factors and their expected timing of development. The plant stages are based on the leaf collar method (Abendroth et al., 2011).

Table 1. Summary of abnormal ear symptoms, their causal factors, and development timing. Source: Ortez et al., 2022c.
Table displaying abnormal ear symptoms, their causal factors, and expected development timing.
Click table image to view/download PDF.

Symptom 1: Tassel Ears

Description: ears at the top of tiller plants in place of tassels

Causal factor(s): lower populations, end or border rows, growing point damage, and genetics

Development timing: initiation and differentiation of tiller’s apical meristem into floral structure

Three photos labeled A, B, and C sequentially. A displays a close up of top of plant with tassel fully replaced by an ear. B and C display close ups of tassels on tillers.
Figure 1 (click to view enlarged image). (a) Complete replacement of tassel and (b–c) partial replacement of tassel on tillers in an end row. Photos by (a) Osler Ortez and (b–c) Robert Nielsen.

Symptom 2: Fasciated Ears

Description: increased and irregular kernel rows

Causal factor(s): specific mutants (i.e., genetics) and cold temperatures

Development timing: ear initiation and development, V4–V7

Two photos, sequentially labeled A and B. A displays a side view of an irregularly shaped popcorn ear with several branches. B displays a top-down view of the same ear.
Figure 2 (click to view enlarged image). Fasciated popcorn ear with seven ear branches. (a) Side and (b) top views. Photos by Osler Ortez.

Symptom 3: Arrested Ears

Description: ear development arrested or stopped prematurely

Causal factor(s): applications of nonionic surfactant (NIS) formulations

Development timing: during the ear size determination period, V6–V12; and up to V16

Three photos, sequentially labeled A, B, and C. A displays an arrested ear on a corn stalk. B is a close up of an arrested ear removed from the plant. C displays three arrested ears with different sizes.
Figure 3 (click to view enlarged image). Arrested ear development likely caused by nonionic surfactant (NIS) applied during mid-to-late vegetative stages (V6–V16, six to 16 collared leaves). Photos by (a) Osler Ortez, (b) Robert Nielsen, and (c) Peter Thomison.

Symptom 4: Pinched Ears

Description: abrupt change to fewer kernel rows in the ear

Causal factor(s): cell division inhibitors, for example, sulfonylurea herbicides

Development timing: ear size determination period, V6–V12

Three photos, sequentially labeled A, B, and C. A displays a side view of an ear with a reduction of kernel rows on the upper section. B and C display ears at the V9  and V12 stage, respectively.
Figure 4 (click to view enlarged image). Corn ears at different developmental stages. (a) Mature pinched ear due to sulfonylurea herbicide applied between V7 and V10 stages, (b) developing ear at the V9 stage, and (c) developing ear at the V12 stage. Visuals adapted from Strachan (2010). Photos by (a–b) Antonio Perdomo and (c) Stephen Strachan.

Symptom 5: Blunt Ears

Description: noticeably shorter and stunted ears

Causal factor(s): plant stressors (e.g., chemicals or environment), genetics, and management

Development timing: ear size determination period, V6–V12

Two photos, sequentially labeled A and B. A displays a short ear lying on its side in front of a longer, normal ear. B displays an overhead view of five, short, ears that are progressively shorter from left to right (low to high degree of stunted development).
Figure 5 (click to view enlarged image). Blunt ears, beer-can ears, or stunted ears. (a) The similarity in kernel row number of a blunt ear (with stunted development) compared with a normal ear. (b) Different degrees of stunted development in blunt ears. Photos by (a) Robert Nielsen and (b) Peter Thomison.

Symptom 6: Silk-balled Ears

Description: silks fail to elongate toward the ear tip properly

Causal factor(s): cold temperatures, drought, and genetics

Development timing: silk elongation, V12–R1

Three photos, sequentially labeled A, B, and C. A displays the twisted appearance of silks on the end of an ear. B is a close up of an ear with twisted silks. C is an overhead view of four ears of corn laid side-by-side, with each ear displaying progressively less corn kernels likely due to silk development issues, moving from right to left.
Figure 6 (click to view enlarged image). (a–b) Silk-balled ears or scrambled silks show silks growing in different directions trapped within the husk, and (c) ears with various severity levels of damage. Photos by Robert Nielsen.

Symptom 7: Incomplete Kernel Set

Description: poor or scattered kernel set in the ear

Causal factor(s): silk damage, drought, high temperatures, pollination issues, phosphorus shortages, herbicide injury, and cloudy days

Development timing: pollination, VT or R1; and early reproductive stages, R1–R3

Three photos, sequentially labeled A, B, and C. A is an overhead view of five ears lying side-by-side, with each ear having less kernels moving from left to right. B displays a close up of the top of an ear, showing clipped ends of the ear’s silks. C displays an ear growing on the plant with clipped silks.
Figure 7 (click to view enlarged image). (a) Ears displaying incomplete kernel set; and (b–c) silk-clipped ears with damage caused by insect clipping before or during pollination. Photos by (a) Peter Thomison, (b) Robert Nielsen, and (c) Osler Ortez.

Symptom 8: Banana Ears

Description: the curvature of the cob toward a damaged ear side

Causal factor(s): severe weather, chemical applications, heat or drought, and stink bug injury

Development timing: pollination, VT or R1; and early reproductive stages, R1–R3

Three photos, sequentially labeled A, B, and C. A, B, and C display banana-shaped ears, all showing kernel damage or lack of kernels.
Figure 8 (click to view enlarged image). Banana ears exhibit curvature along the cob shape with different degrees of damage (A, B, C). Husk leaves were removed (if needed) for better symptom visibility. Photos by Osler Ortez.

Symptom 9: Zipper Ears

Description: ears with missing kernel rows

Causal factor(s): higher seeding rates, drought stress, genetics, defoliation, and deficient pollination

Development timing: pollination, VT or R1; and early reproductive stages, R1–R3

Three photos, labeled sequentially A, B, and C. A is an overhead view of nine ears that are progressively smaller and have irregularly shaped missing kernel rows moving from left to right. B is a corn ear on the plant, showing missing kernel rows in one side of the ear. C is a side view of an ear that is missing multiple kernel rows.
Figure 9 (click to view enlarged image). (a) Zipper ears increase at higher seeding rates; from left to right (three ears per treatment): 25,000, 35,000, and 45,000 seeds per acre. (b) Ear with several kernel rows missing due to pollination or abortion issues. Husk leaves were removed for better symptom visibility. Photos by (a) Peter Thomison, (b) Osler Ortez, (c) Robert Nielsen.

Symptom 10: Tipped-back Ears

Description: missing kernels at the tip of the ear.

Causal factor(s): pollen and silk availability, kernel abortion, cloudy days, heat, drought, genetics, and higher seeding rates

Development timing: pollination, VT or R1; and early reproductive stages, R1–R3

Four photos, sequentially labeled A, B, C, and D. A is a corn ear with nearly half its kernels missing. B is an ear with about a quarter of its kernels missing. C is an ear with about ten percent of its kernels missing. D is an ear with about five percent of its kernels missing.
Figure 10 (click to view enlarged image). Tipped-back ears with unfilled kernels toward the tip. (a) Ear with about 50% tipped-back, (b) about 25% tipped-back, (c) about 10% tipped-back, and (d) about 5% tipped-back. Husk leaves were removed for tip-back visibility. Photos by (a, b, and d) Osler Ortez and (c) Justin McMechan.

Symptom 11: Multi-ears per Node

Description: multiple ears at individual stalk nodes or same ear shank

Causal factor(s): environmental stress (e.g., cold), low seeding rates, genetics, damage to primary ear

Development timing: after ear initiation (V4–V6) and before pollination (VT or R1)

Five photos, labeled sequentially A, B, C, D, and E. A and B show two ears of corn growing from the same shank. C shows four ears of corn growing from the same shank. D shows six ears of corn growing from the same shank. E shows three ears on the same ear shank.
Figure 11 (click to view enlarged image). Multi-ears with more than one ear on the same ear shank. (a and b) Two ears, (c) four ears, (d) six ears, and (e) three ears. Photos by (a–d) Osler Ortez and (e) Robert Nielsen.

Symptom 12: Barbell Ears

Description: missing kernels and diameter decrease in the cob

Causal factor(s): temperature stress, limited solar radiation, ethylene, hormones, chemical applications, genetics, and damage to primary ear

Development timing: during ear size determination period, V6–V12, and up to R1

Four photos, labeled sequentially A, B, C, and D. A shows an ear with no kernels and dramatic deformation on the ear’s base. B shows an ear with kernels missing from the middle. C shows an ear with kernels missing from the top of the ear. D shows an ear with missing kernels from its middle portion. All of them show dramatic deformation to the inner section of the ear, the cob.
Figure 12 (click to view enlarged image). Barbell ears— kernels missing in specific sections of ears. (a) Kernels missing on the base of the ear. (b) Kernels missing toward the middle. (c) Kernels missing toward the tip of the ear. (d) These symptoms are accompanied by significant cob diameter decreases. Photos by (a–c) Osler Ortez and (d) Robert Nielsen.

Symptom 13: Short-husk Ears

Description: shortened husk leaves with ears protruding beyond the husks

Causal factor(s): short-term stress, for example, heat or drought followed by cooler temperatures and precipitation, high-speed winds or storms, and genetics

Development timing: close to tasseling and pollination, V18–R1

Four photos, labeled sequentially A, B, C, and D. A, B, and C show ears with incomplete husk cover progressively moving left to right. D is an ear with the top half of the husk missing.
Figure 13 (click to view enlarged image). Short-husks ears and, thus, kernels are exposed to varying degrees. (a) About 10% of cob/kernel exposure, (b and d) about 50% of cob/kernel exposure, and (c) about 90% of cob/kernel exposure. Photos by (a–c) Osler Ortez and (d) Robert Nielsen (d).

Summary

Intensive study for over 100 years has resulted in a good understanding of corn growth and development, but knowledge gaps remain. Limited information on several abnormal ear symptoms and the unknown reasons for their specific causes highlighted the need for more research. Crop exposure to unfavorable conditions can negatively affect ear formation, produce abnormal ears, and ultimately reduce yields and profits.

With available knowledge, abnormal ears can be seen as the result of an “expression triangle” where susceptible hybrids (genetics), conducive environmental conditions (environment), and unfavorable management practices (management) interact and result in abnormal ears. Ear abnormalities are detrimental to grain yield and quality, and their mitigation is imperative to achieve sustainable corn systems.

For more information and pictures on abnormal ears, visit u.osu.edu/mastercorn.

For questions on corn and abnormal ears, email Osler Ortez at ortez.5@osu.edu.

For more information on the author, Osler Ortez, go to hcs.osu.edu/our-people/dr-osler-ortez.

References

Abendroth, L. J., Elmore, R. W., Boyer, M. J., & Marlay, S. K. (2011). Corn growth and development, PMR 1009. Iowa State University Extension.
store.extension.iastate.edu/product/Corn-Growth-and-Development

Ortez, O., McMechan, A. J., Robinson, E., Hoegemeyer, T., Howard, R., & Elmore, R. W. (2023). Abnormal ear development in corn: Does hybrid, environment, and seeding rate matter? Agronomy Journal.
doi.org/10.1002/agj2.21338

Ortez, O. A., McMechan, A. J., Hoegemeyer, T., Rees, J., Jackson-Ziems, T., & Elmore, R. W. (2022a). Abnormal ear development in corn: A field survey. Agrosystems, Geosciences & Environment, 5(1), e20242.
doi.org/10.1002/agg2.20242

Ortez, O. A., McMechan, A. J., Hoegemeyer, T., Ciampitti, I. A., Nielse, R. L., Thomison, P. R., Abendroth, L. J., & Elmore, R. W. (2022b). Conditions potentially affecting corn ear formation, yield, and abnormal ears: A review. Crop, Forage & Turfgrass Management, 8(2), e20173.
doi.org/10.1002/cft2.20173

Ortez, O. A., McMechan, A. J., Hoegemeyer, T., Ciampitti, I. A., Nielsen, R., Thomison, P. R., & Elmore, R. W. (2022c). Abnormal ear development in corn: A review. Agronomy Journal, 114(2), 1168–1183.
doi.org/10.1002/agj2.20986

Thomison, P., Lohnes, D., Geyer, A., & Thomison, M. (2020). Troubleshooting abnormal corn ears. Ohio State University Extension.
u.osu.edu/mastercorn/

Originally posted Jul 24, 2023.
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