Abnormal Ear Development in Corn

Corn ear abnormalities have been reported for many years. A normal dent corn hybrid in the U.S. usually develops one productive ear per plant. A normal ear generally produces 16-18 kernel rows with potential for about 800-900 kernels per ear (<600 kernels successfully mature due to pollination failure and kernel abortion) and have viable silks that extend beyond the husk during early reproductive stages. Abnormal ears may contrast a normal ear with varying symptoms, some of which are generally described below. It is suggested that interactions of genetics, environment and management practices may increase the frequency and severity of corn ear abnormalities.

Types of Corn Ear Abnormalities
Blunt Ear Syndrome (Arrested Ear or Hollow Ear Development)

Also referred to as “beer-can ear”.

• Symptoms:
  • Reduced ear size and kernels per row, normal ear formation abruptly ends leaving only a few to no basal kernels develop
  • Husk length and number of kernel rows are normally unaffected
  • May be associated with multiple ears per node
• Causes:
  • Development of initial ear likely disrupted by a single triggering stress occurring at a very specific time during ear development several weeks prior to pollination
  • Rapid drop in temperatures as low as 40-50° F occurring during row number determination stages (V5-V12) followed by warming conditions are speculated to injure meristematic tissue within the ear shoot, ceasing cob and embryo development
  • Researchers have also reproduced symptoms by applying a single application of nonionic surfactant at V12-V14 growth stages — symptoms were not observed when only applying fungicide at similar growth stages
  • Similar ear symptoms can be observed when Multiple Ear Syndrome is present

Unfilled Ear Tips (Tip-back or Tip-dieback)

• Symptoms:
  • Missing or shrunken kernels toward the tip of the ear and progressing downward
• Causes:
  • Later developing silks unable to receive pollen due to delayed emergence, drying out or insect clipping
  • Environmental stress conditions such as high temperatures, severe drought, reduced solar radiation, foliar diseases and nitrogen deficiencies often cause fertilized kernels to abort due to insufficient sugar and starches needed for proper grain fill
  • Younger kernels at tip of ears are more vulnerable to aborting from stress occurring early in grain fill process

Incomplete Basal Fill

• Symptoms:
  • Unpollinated kernels at the base of the ear
• Causes:
  • Silk emergence began prior to start of pollen shed
  • First emerging silks were desiccated from drought or heat stress and unable to receive pollen
  • Selective silk clipping by insects such as corn rootworm beetles

Zipper Ears (Banana Ear)

• Symptoms:
  • Partial or entire rows of kernels absent or stunted
  • Ear may be curved or misshaped from the lack of developing kernels on that side of the ear
• Causes:
  • Poor pollination or kernel abortion following pollination, often from environmental stressors
  • Interplant competition for water and nutrients causing kernel abortion (observed in higher seeding rates)
  • Defoliation injury after pollination

Incomplete Kernel Set (Scattered/Poor Kernel Set)

• Symptoms:
  • Reduced or scattered kernel set with a limited number of kernels on the ear
• Causes:
  • Failed pollination likely from asynchronous pollen shed, inadequate pollen supply or clipped silks (insect or mechanical damage)
  • Severe drought and high temperatures
  • Kernel abortion from stressors that significantly reduce plant photosynthesis

Unpollinated Ear (Missed Nick)

• Symptoms:
  • Normal cob development without any kernels present
• Causes:
  • Pollen shed and silk emergence timings were not synchronized due to environmental stress such as drought delaying silk emergence while pollen shed continues at normal timing
  • Severe silk clipping from insects prohibited silks receiving pollen

Multiple Ear Syndrome (Bouquet Ears)

• Symptoms:
  • Multiple ears develop at the same ear shank and the ears usually have fewer kernels developing

• Hypothesized Causes:
  • Corn hybrid genetics may play a role
  • Environmental stressors (extreme temperatures) or chemical stressors during early ear formation
  • Loss of primary ear shoot dominance from damage

Barbell Ears (Pinched Ears)

• Symptoms:
  • Usually kernels on one or both ends of the cob with a pinched appearance middle of the cob
• Causes:
  • Ovule abortion in early ovule development from a stressor
  • Combination of susceptible genetics and an environmental stressor
  • Stressors include temperature (chilling), specific ALS herbicides and plant hormone abnormalities occurring in the V7-V10 growth stages

Translucent Kernel

• Symptoms
  • Random fertilized kernels with a clear or translucent kernels spread randomly amongst a normal sized ear
  • Clear kernels collapse as they begin to mature, leaving a shrunken shell
• Causes:
  • Often associated with late or off label glyphosate herbicide applications

Insect Injury

There are many insects that may cause damage to developing corn ears leading to various symptoms. Insect feeding on developing ears, silks and kernels have the potential to cause malformed ears and reduce kernel quality. Insects include corn rootworm beetles, Japanese beetles, stink bugs, Western bean cutworm, corn earworm and European corn borer, etc.

There are more corn ear abnormalities not described here. Overall, environmental factors such as drought, high temperatures, lack of nutrients, or chemical applications may cause significant stress plant development leading to unusual corn ear abnormalities. If you have questions or would like more information on abnormal ear development, please reach out to your local Golden Harvest sales representative or agronomist.