Corn silking by calendar date

Does early silking result in higher yield? Good stories always have a critical point where survival of the main character hangs in a precarious balance that may either turn out good or bad.

Some readers skip ahead to see how it comes out; others accelerate their reading pace in a more systematic fashion. Still, others keep plodding along, word by word, page by page. All three systems work. Not many of us would stop reading.

How would we react if we got to the critical point in the story and find the end of the story unwritten! Disappointed, frustrated? We are now at that critical point in the 2011 corn story.

Corn is the leading actor in a story written every growing season in thousands of fields across Iowa. If forced to choose only one critical point, the time when the crop’s future dangles on the brink of success or failure, it is silking.

Planting progress 2011

Iowa’s 2011 planting progress matched that of the five-year average of 1975-79 — more than 30 years ago! In contrast, in 2010 we had some of the fastest planting progress in Iowa’s history. Does our slow start spell disaster for the 2011 corn crop?

As I mentioned in this column last month, “We may not have lost any corn yield potential as a result of our extraordinary 2011 planting season. Although we know the importance of planting date, conditions at planting and those that immediately follow are even more important. The remaining growing season strongly influences final yields.”

Nevertheless, many agronomists understand that early planting and silking often combine not only for good yields but also lower grain moisture. However, is this always true?

Timing is everything

Historical silking date and yield records from USDA’s National Agricultural Statistics Service provide considerable useful data to address this question (see graph). Yield trends continue to increase at more than 2 bushels per acre per year as a result of improved genetics, better crop and soil management, and weather conditions.

Planting dates over these same periods averaged about three days earlier for every 10 years (data not shown). In contrast, the silking trend over these years averages about one day earlier every 10 years.

Earlier silking in part is associated with earlier planting. In addition, early silking is loosely correlated with higher yields. However, many exceptions to this occur.

For example, although we had relatively early silking dates from 2005 to 2007 and again in 2010, silking nearly a week later in 2009 resulted in the highest corn yield in Iowa’s history. Our second-best yield occurred in 2004, which silked about the same time as those of 2005-07, and 2010.

Many environmental factors come into play during the 35 days or so that Iowa’s corn crop silks. Until the critical point of the 2011 corn story is experienced, the outcome is uncertain. And even then, much of the growing season’s story remains untold as grain fill occurs and maturity reached.

Elmore is the Iowa State University Extension corn agronomist.

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Iowa corn yields and silking dates, 1981-2010


YIELD VS. SILKING: Early silking is no guarantee of higher yield, as just about anything can happen to affect final yield. Yields are marked with red squares, with the y-axis for yield on the far right. The left vertical axis records silking dates. The dark open circles mark the date at which half of Iowa’s corn was planted. The vertical black lines mark the range of silking in each year. Source: Data adapted from USDA-NASS

This article published in the July, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.