Dr. Dan Talks Agronomy

An agronomist in central Illinois recently sent me an email reporting corn ears with 16 or even 18 rows around but limited length, only 20 to 22 kernels long. They were "beer-can ears that you could throw like a baseball," he said. They "can be found in a wide variety of hybrids and companies. Some treated with a fungicide and some not. (Symptoms are) usually found about half way between the drowned-out spots and the top of the hill where the good corn is."

The agronomist told me over the phone that these blunt ears were completely filled to the tip but just short and lacked kernels. He wondered if water damage or water-logged soils at an early growth stage or if limited nitrogen or some micronutrient or an inability to take up phosphorus in wet soils could be a factor. He said phosphorus and potassium soil-test levels are very good in these affected areas.

The term "beer-can ear" isn't new; an internet search reveals hits dating back 20 years. The affliction also goes by the terms such as blunt ear, pinched ear and others. The term that best describes what has happened, however, is "arrested ear development."

What arrests ear development? In the past decade beer-can ear was associated with applying a herbicide and a fungicide during early vegetative development that affected development of the corn ear. It was eventually determined that the culprit wasn't the fungicide or herbicide but the interaction of crop stage and the adjuvant in the crop chemical mix. Today, growers are safe applying these cocktails as long as they do it between V5 and V7 and before V8 -- or they can just remove the adjuvant. However it is important to point out that at V8 and V9 the ear is very vulnerable to sudden stresses.

With arrested ears the row numbers around the ear are normal. Kernel number per row is what is affected. Kernels develop as normal at the butt end of the ear, but about half way up the ear kernel development just stops. Ears have 15 to 20 kernels per row compared to a normal 35 to 40.

To determine what might cause arrested ears, we first have to think about ear development. At the V6 collared leaf stage the corn plant is determining the number of kernel rows around. A typical row count would be 16 and 18, though 14 to 20 rows around are considered normal. By V10 the number of kernels per row is determined. A normal kernel count would be 35 to 40. At the V10 to V12 stage ear shoots are visible on the plant. But only the ear shoots higher on the plant develop into harvestable ears.

Arrested ear development happens when there is some stress affecting the plant at or just after V8 when the plant is determining kernels per row. Purdue University corn expert Robert Nielsen pointed out in a 2001 web article, "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." Of course application of the wrong pesticide or cocktail of products would also be considered a triggering event.

Nielsen also pointed out that a chilling injury could cause arrested ears and cited an example in 2001 when nighttime temperatures dropped into the 40s at the V8 to V9 stage. Similar conditions and symptoms were reported in 1992 and 1996.

What was the weather back in June 2015? It was cool, cloudy and rainy with cool nights. During the first week in June, nighttime temperatures in parts of central Illinois dropped below 50 F.

Interestingly, the Illinois agronomist pointed out the symptoms were usually found halfway between drowned out spots and the top of a hill. This suggests an interaction between stage of plant development and chilling injury associated with a drop in nighttime temperature below 50 F.

During June, the corn plant is laying down a new leaf stage every two days. You may not see this visually during routine field checks; collared leaves appear at the rate of about one collar per week. So the corn fields in question could literally have had parts of the field at V6 to V7 (drowned, slow growth spots) and V10 to V12 (hill tops), neither which were hurt by the cold temperatures. Plants in between, which were at V8 to V9, were most vulnerable to chilling injury.

As Nielsen has mused in his articles, beer-can ear is an oddity, not common and often can't be clearly explained. In the recent Illinois situation there seems to have been an odd combination of events including variable soil wetness due to excess rain, delayed plant development and cold nights that triggered arrested ear development in particular regions of the field when plants were at their most vulnerable state. This probably won't happen there for another 50 years.

Nielsen's 'Beer Can' Ear Syndrome -- 2001' and 'Blunt Ear Syndrome in Corn' articles can be found at https://www.agry.purdue.edu/… and https://www.agry.purdue.edu/…, respectively.

(GH\CZ\SK)

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