This troubleshooting Garden Guide follows others in our Sweet Corn Garden Guide Series.
Agronomists have been researching sweet corn crops for decades. They have learned that both biotic & abiotic factors can influence yield, ear development, and quality. In this guide, we discuss different types of ear development disorders, their causes, and avoidance measures when possible.
- Common biotic (living) factors that affect growth are things like insects, animals, fungi, or bacteria.
- Abiotic (non-living) factors that affect ear development include heat, cold, drought, excess moisture, and hail, as well as other growing conditions such as nutrient imbalances, or applications of chemical pesticides or herbicides.
- It is important to realize that abnormal ear development issues typically occur due to a combination of these different biotic and abiotic factors, not just one.
It is important for growers to understand that ear abnormalities or deformities are not due to the seed itself. All a seed can do is germinate. These are plant abnormalities caused by any number of outside influences, as mentioned above. These issues can happen in any field any given season, to any hybrid sweet corn variety. They are classified as disorders, not diseases. Although diseases can also affect ear development and quality.
Over many years of study, agronomists have gathered valuable information about sweet corn ear abnormalities. Listed here are 10 abnormalities that occur most commonly.
Arrested Ears or Blank Ears
Ears form with no kernel development. All cob, with few to no kernels.
- This is a pollination problem, where the silk development process is impaired, or ovules are not receptive to pollen, which causes no kernels to form on some or most of the ear.
- Main causes are still unknown, but agronomists believe this relates to adverse physical or environmental conditions occurring around V10 to V15 growth stages. Some differences in this disorder can exist between different hybrids.
- Because this is thought to be a highly weather-related phenomenon, it may not occur in successive seasons, but if a certain hybrid variety seems susceptible, try a different variety.
Banana-shaped ears develop.
- These deformed ears are caused when entire rows or a partial kernel row are aborted (fail to form).
- Causes are not completely clear yet, but this condition follows weather stresses, misapplication of herbicides, or from heat & drought conditions, especially before or at pollination stages (VT - R1/R2).
Multiple ears form on the same node or ear shank.
- A cluster of ears or a bouquet of multiple ears grows with kernels that mostly fail to form.
- Causes for this condition include heat stress during early ear formation during V5 to V15 growth stages.
- The lack of kernel formation is due to timing interruptions between silks and pollen shed.
- This condition can also be caused by misapplication of herbicides, fungicides, or insecticides prior to silking during V10 to VT stages. Avoid applications of these products during these growth stages.
- Some varieties appear to be more sensitive to forming Bouquet Ears than others. If this issue continues for several years in a row, try a different variety that may be better suited to the environment.
Ear Stunting or Blunt Ear Syndrome
Colloquially known as "Beer Can Ears"
Stunted ears are much shorter in length than a normal ear, while the number of rows may not be terribly affected. But since the physical size of the cob is shorter, the total number of kernels per ear is less.
- Since ear size is determined during the mid-to-late vegetative stages (V4 to V18), any stresses (biotic or abiotic) during this period of development could lead to stunted ears.
- This abnormality can relate to the misapplication of chemicals like fungicides, insecticides, or herbicides, especially if applied at sensitive times, although the primary cause has not yet been isolated.
Ear tips elongate past the end of the husks, leaving the ear tips and kernels exposed to the elements.
- Exposed ear tips and kernels are susceptible to disease, pests, heat, and drought or hail.
- Primary cause is related to weather stresses before and during pollination (mostly heat & drought).
- However, agronomists have noted this condition seems to happen most frequently when plants become stressed by heat & drought during pollination when this is followed by cooler, wet weather patterns.
- This abnormality should not be confused with Tip Dieback (Discussed below).
Poor or Spotty Kernel Set
Degree of severity can range from just a few kernels missing to ears with hardly any kernels, leaving most of the cob showing.
- Spotty kernel set relates directly to a lack of pollination, fertilization failures, or ovule abortion after pollination.
- List of factors in order of probable cause:
- Warm temperatures.
- Lack of water, especially during warm temperatures.
- Poor pollination (which can happen for many reasons).
- Any biotic or abiotic stresses affect pollen shed or silk development (V10 to R1).
- Poor timing between pollen shed and silking which directly affects pollination.
Essentially ears grow at the top of a stalk where tassels normally form.
- Tassel ears can appear in several forms, degrees, and sizes, with or without full tassel development.
- While the exact causes are not fully known yet, this fairly common deformity is definitely weather-related; therefore, adverse environmental conditions are the leading cause.
- This disorder is quite common in tillers (See below), also common in stalks along field edges, and appears more often in plantings of lower density (number of plants/acre).
- Tassel ears, even if fully formed, will typically be void of husks which leaves the kernels exposed to the sun, insects, and pathogens.
Ears with poor kernel set that is isolated to the tips of the ears.
- Tip dieback becomes noticeable after pollination and relates to poor pollination factors.
- This disorder is due to poor pollination of the ovules, or non-fertilized ovules where pollen is shed when silks were not protruding from the husks and kernel abortion in the weeks following pollination up until the milk stage (R3).
- Biotic causes such as corn rootworm or Japanese beetle disruption, plant diseases, or abiotic stresses such as heat & drought, and nutrient deficiencies (specifically nitrogen stress) which all affect pollination timing between tasselling and underdeveloped or late-developed ovules and silks that leads to poor pollination.
- Tip kernels are the most sensitive to abiotic stress conditions. Have you ever torn a husk off to find missing or imperfect, sunken tip kernels? This is quite common, even in healthy, productive fields.
- Often, kernel abortion at the ear tips occurs later during the grain-filling stages (R2 to R6), which means physical stresses just prior to or during these growth stages should be avoided.
Kernel Red Streak
Kernels near the tip of the ear are streaked with red pigment.
- Red streak disorder is a visually distinctive red coloration in the pericarp of the kernels, mostly at the tip of the ears.
- These red symptoms are caused by wheat curl mites feeding on the kernels whose salivary secretions contain a red pigment. Although this causes unsightly and unappetizing kernels, there is no evidence that this discoloration affects the nutritional value or the flavor of the corn. You won't want to serve it to your grandma, but it can still be used for feed.
Tillers or Suckers
Not an ear issue, but these are branches that develop from axillary buds along stalk nodes.
- Tillers are part of normal corn physiology and typically indicate favorable growing conditions exist.
- Tillers can often occur following early-season injury to the main stalk and are usually random within a crop.
- Tillers themselves do not affect subsequent growth and are best ignored. No reason to remove them.
Ear disorders such as these are typically random in nature and are due mostly to environmental variabilities beyond the grower's control, although growing conditions such as proper nutrition and consistent field moisture play the biggest role in preventing these issues. These disorders often do not affect an entire crop, and they do not usually appear repetitively year to year due to their causal nature. Once an ear abnormality is discovered, the damage has usually been done for that season. Avoidance and preventative measures are the best defense against these random ear disorders.
(Most of this valuable information is courtesy of Kansas State University Research & Extension)