aturday football games in Ross-Ade Stadium, tailgate parties and beer cans; ah, yes, the familiar signs that classes are in session at Purdue again. Interestingly enough, a few corn fields out in the state seem to be supporting the cause by their exhibition of a peculiar oddity known as 'beer can' ears. Also called 'pop can' ears or simply stunted ears, this phenomenon was identified in several fields and hybrids in Wells and Grant counties this past week.
Although the plants and ear shoots (husk leaves) appear normal, the cobs of 'beer can' ears are remarkably short and the tip inch or so is barren. Interestingly, kernel row numbers at the butt end of these ears appear to be normal or at least acceptable. Part way up the ear, however, kernel row number goes from normal to nothing. Compared to an acceptable 35 to 40 kernels per row, these ears only contain about half that in terms of ovules per row and often only 12 to 16 actual kernels per row due to silk balling that occurred when the final silks could not elongate successfully through the remainder of the normal length husk leaves. More severe ear stunting also occurs, leaving one with what looks like a corny hand grenade.
A tassel branch-like appendage sometimes exists at the tip of the cob, 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 in the neighborhood of leaf stages V8 to V9.
Because ear development was apparently arrested or stopped so 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. One possible cause could be the application of certain post-emergence herbicides (growth regulators or ALS-type), but none were applied to the fields I visited last week.
Another possible cause of such a dramatic cessation of ear development could be chilling injury. Indeed, research reported from Belgium (Bechoux et al., 2000; Lejeune and Bernier, 1996) documents the potential for chilling injury at the time of ear and tassel initiation (about V5) to prevent ear initiation altogether and reduce tassel branch and spikelet formation. Perhaps chilling injury to the developing ear a few leaf stages down the road could similarly abort continued ear development.
The nearest weather reporting station to the field I visited in Wells County was at Bluffton. Using the reported daily maximum and minimum temperatures (http://shadow.agry.purdue.edu/sc.index.html), I calculated the daily growing degree days (GDDs) and their accumulation from the reported day of planting (May 8) of this field. Based on earlier research of one of my graduate students that documented the relationship between corn leaf stage development and GDD accumulation (Wuethrich, 1997), I then estimated the leaf stage progression of the corn for that field.
Interestingly, there was a single night of cold temperatures down into the high 40's at about the time the crop should have been at the V8 to V9 stages of development. That leaf stage range is similar to what the length of the cobs suggests was the time of arrested development. Coincidence? Perhaps.
The 'beer can' ear phenomenon has been reported in other years in Indiana. The first rash of reports in dent corn occurred in 1992, that year often lovingly referred to as our 'ice age' summer because of the season-long unusually cool temperatures. The problem was last reported in 1996 in parts of northern Indiana and Ohio, most frequently in fields planted during the last two weeks of May. Several nights of temperatures in the mid- to high 40's were reported that summer during the time when these late-planted fields were also estimated to be at leaf stages V8 to V9.
The fact that this phenomenon does not occur frequently in Indiana probably relegates it to the curiosity shelf along with dumbbell ears, pinched ears, two-headed ears and other corny oddities. However, the possibility that chilling injury may be a contributing factor to its occurrence is interesting from the viewpoint that far less research has been conducted on the injurious effects of cold temperatures on corn reproduction than on those effects due to heat stress or drought.
Bechoux, N., G. Bernier, and P. Lejeune. 2000. Environmental effects on the early stages of tassel morphogenesis in maize (Zea mays L.). Plant, Cell & Environment. 23(1):91-98.
Lejeune, P. and G. Bernier. 1996. Effect of environment on the early steps of ear initiation in maize (Zea mays L.). Plant, Cell & Environment. 19:217-224.
Nielsen, R.L. (Bob). 1996. Beer-Can Ear Syndrome in Corn. Purdue Pest & Crop Newsletter. 30 Aug. 1996. Also on the Web at www.kingcorn.org/news/articles.96/p&c9645.htm.
Nielsen, R.L. (Bob). 1996. Another Example of Beer-Can Ears in Corn. Published at the Chat 'n Chew Café on the Web at www.kingcorn.org/news/articles.96/rn9601.htm.
Wuethrich, Kirby. 1997. Vegetative and Reproductive Phenology of Fourteen Hybrids of Dent Corn (Zea mays L.). M.S. Thesis. Purdue Univ., W. Lafayette, IN.