Blunt Ear Syndrome (BES) in corn, sometimes also referred to as "Beer
Can Ear" Syndrome, is a curious oddity that occurs from time to
time throughout the corn growing areas of the U.S. The major symptom
of BES, unusually short ears, is the consequence of arrested ear development
that likely occurs during the ear size determination period prior to
pollination. Researchers at Colorado State University have devoted the
most energy to investigating this problem, but the causes of the arrested
ear development have not been conclusively identified.
Interestingly, the symptoms of BES appear to be restricted primarily
to the development the ear. Other aspects of plant appearance (stalks,
leaves, husks) are normal in every respect until later in the season when
plants with severely arrested ears turn shades of red and purple in response
to an overabundance of plant sugars in the leaf and stalk tissues.
The cob of a "beer can" ear is remarkably short and the tip
inch or so is often barren. Interestingly, kernel row number at the butt
end of these ears appears to be reasonably normal. Part way up the ear,
however, cob and kernel row development simply cease. Compared to a fairly
typical 35 to 40 kernels per row, BES ears exhibit about half that length
in terms of ovule number per row and often only 12 to 16 developed kernels
per row. Silk balling, that occurs when the final silks do not successfully
elongate through the remainder of the normal length husk leaves, causes
the lack of kernels at the tips of BES cobs. More severe forms of BES
occur from time to time, leaving one with what looks like a corny hand
grenade.
The tip of a BES cob sometimes exhibits a tassel branch-like
appendage, while other ears exhibit an apparent remnant ear initial similar
to that visible by dissection of ear shoots at about leaf stage V9 (nine
visible leaf collars). The latter symptom suggests that development of
the ear initial was interrupted or arrested between the time ear initiation
occurred (about V5) and kernel row number was finalized (about V12). The
half-length size of the cobs suggests that ear development was stopped
at approximately leaf stages V8 to V9.
Possible Causes of BES
Because ear development is arrested or stopped completely and
suddenly (normal row numbers, then nothing), the cause of the problem
would appear to be a single triggering event, not a lingering stress like
nutrient deficiency or soil pH. One possible cause of BES could be the
application of certain post-emergence herbicides (growth regulators or
ALS-type) during the period of row number determination (V5 - V12). While
possible, this cause can be ruled out because of the diversity of herbicide
programs encountered in documented cases of BES.
Another possible cause of such a dramatic termination of ear
development is chilling injury. Indeed, research reported from Belgium
documented that chilling injury at the time of ear and tassel initiation
(about V5) could prevent ear initiation altogether or reduce tassel branch
and spikelet formation. Perhaps chilling injury to the developing ear
at somewhat later leaf stages could similarly arrest further ear development?
The term "chilling injury" does not necessarily translate simply
to frost events. Temperatures in the high 40's to low 50's may be sufficient
to injure meristematic regions of the corn plant, especially if temperatures
during the days preceding the chilling injury were warm to excessively
warm.
--Bob Nielsen, Department of Agronomy, Purdue University |
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