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:
- 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).
- Abnormal ears reduced grain yield 35–91% (yield loss per area depends on the symptom, its frequency, and its severity).
- 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:
- ear number per unit of area (early in the season)
- kernel number per ear (mid-season)
- kernel weight (late in the season)
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).
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
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
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
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
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
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
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
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
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
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
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)
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
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
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/